How do I solve this booting problem?

Did you try re-booting?

yes

Try this discussion.

From the GRUB command line, the first thing you will want to accomplish is pointing GRUB at the correct partition to find your desired kernel. If you already know which partition this is, then great- for example, on my laptop running Puppy Linux the boot partition was /dev/sda1. For reasons which are probably best left unexplored, GRUB uses a different nomenclature for block devices from the one used by Linux. In GRUB /dev/sda1 is called hd(0,1).
If you don’t know already which partition it is, then you can use the “find” command to do: find /vmlinuz or find /boot/grub/ and it will respond with the device name (for example, hd(0,1) as above). Also remember that GRUB supports tab completion: you can just type: root hd([TAB] and GRUB will automagically give you a list of partitions to choose from.

Once you’ve selected the proper “root” partition to boot from, choose your kernel:
kernel /boot/[TAB]
And GRUB will show a list of kernels in that directory. Pick one that you know works. If you aren’t sure, pick the one with the highest version number. The command line should wind up looking like this:
kernel /boot/vmlinuz root=/dev/sda1
where “vmlinux” means the kernel you chose and /dev/sda1 represents the root filesystem of your system. Since this will be passed as a boot option to the kernel, you use the Linux device-naming convention.
Once this is done, just type:
boot
and GRUB should boot your system, provided there aren’t any dependencies that I haven’t covered. If you have problems feel free to post here, to PM me, or you can google “boot from grub command line” which is how I figured out how to get my lappy working when the GRUB menu didn’t work.

I understand you don’t have an Ubuntu Live CD, but it’s very very easy to get one. You should do so as soon as you can.
Also, most USB disk images are also live systems which work as well as or better than the CD. Do you still have the USB disk you installed from? It’s good to keep such a device around, as it makes a wonderful diagnostic tool.

Sounds like your hard drive isn’t talking. Check the connections to it, power and data. Reseat those connectors (take ‘em out, shove ‘em back in).
Check your power supply, you might have a blown 12V section in the PS. Most of the system will run on lower voltage than the drive, it will wake up and not find the drive.

If you’re lucky your laptop has a hatch on the bottom for access to the harddrive.
Otherwise doing these checks might mean substantial disassembly. Try to find disassemly instructions online for your model and have your eensy weensy screwdrivers ready and a mat or box or…. to keep all the little screws in etc.

@dabbler Unless the bootable partition is on a separate device from the GRUB installation the fact that GRUB is coming up at all means that the hard drive is talking at least a little bit.
It’s certainly possible that the boot partition is fried, but if @Anatelostaxus has only one HDD in the computer I think we can rule out a hardware problem in this case.

@koanhead @dabbler &
@SpatzieLover @crisw

Well guys, (first of all thank you for helping me).. I’m paying close attention to your suggestions trying to figure out a way.
Now, the bootable HD containing the OS (Ubuntu 10.4) is an external device that I occasionally would swap from one PC to another, (at times also installing into the laptop, instead of connecting it externally).
I’m quite sure I’d formatted it previously to only ONE partition. One big chunk of space all for the main OS, which I chose to be Linux when still battling with former complications with a double partition Ubuntu / vista.

It is very important that I recuperate the data on my gnome desktop and all the firefox data.

@koanhead I’m trying to do what you suggested right now. I’ll let you know. Please follow me afterwards… need guidance! D=

@dabbler Yes, indeed I have fiddled with the connectors quite a bit. Which is what in the end lead me to extracting the HD out of its case and installing into a laptop I’d been using it in.

@both of you (and anyone else): The OS had been playing a neat trick on me, (the little bastard..)
I would leave it on over night (performing action which require a lot of time. Every now and then i’d just find it stalling in the morning when I would try to wake it up.The little green light on the case would be flashing madly. The only thing I could do was switch off the computer. That’s the last thing that happened before it went on holiday.
I know I might have treated it uncautiosly from time to time, though I was generally very caring of it. I kept it “clean” and all. I relly love the poor thing. I just needed it to do things for me that I could spend time doing during the day, ‘cause of work.
Gobshite.. just to think about all the time, effort, study passsion and dedication I’d invested into forming my little portable OS… It can’t all be wasted.

@koanhead Very well, I’ve tried the procedure.. but.. it doesn’t even work right from the start.
At every attempt to put in a command, it says:“Unknown command” this, “Unknown command” that… Yes, I still have the bootable USB drive witht he ISO CD image. I tried it yesterday, but it didn’t seem to work from the “try it out” version.

Hm. Can you tell me what happened when you tried the “try Ubuntu” from your USB drive? What specific error messages you got, or any strange behavior you noticed?
Do you have another computer handy that you can use to download and burn a live cd?

Have you tried “help” at the GRUB command line?

Don’t worry about your data just yet. It’s probably easily recoverable even if the /boot partition is hosed.
It’s a bad idea to turn off the machine that way though, as you’ve found out. Do you know about the magic SysRq key? If nothing else works, it can save your bacon.

@koanhead Well, when I tried it the first time I didn’t really notice any strange behaviour..
Not even the second time, which is now as Iam using it to gain access to the net.
I’ve burned the live CD and am operating with it now. One interesting thing is that I opened Gparted, Disk utility and the “install ubuntu 10.4” option, all found in the system/administration menu. The first software identifies the HD containing my beloved OS with “boot” flag. The second reads the Hds presence as well and finally the installation identifies the HD but it finds no operating system present.
I’ll try the “help” command at grub, now.
I don’t quite know how to use either the grub command line, nor the sys req procedure.. Looking into it now.

@Anatelostaxus You wrote that the USB drive “didn’t seem to work from the ‘try it out’ version”. Not working counts as strange behavior. In order to help troubleshoot it we need to know exactly how it’s not working. Is it hanging up? Does the screen go blank? Are there error messages?
And then you go on to say that you are now using it- which means it worked. Did it suddenly start working? Did you do anything different?

In any case, it’s good that it works and that you have a live environment to use.
It’s best, if possible to not try to tell us what the programs say to you. Cut and paste if possible, or take a screenshot (Alt-PrtScn) and post it on imgur or some such so that we can look at it. It’s a lot easier for those of us who are used to dealing with these programs to parse the output rather than try to guess it from someone else’s interpretation.

I’m not quite sure how the installer goes about determining the OS of a partition. There are two possibilities that come to mind: the filesystem type (which parted also reports) or the presence of a kernel. If your filesystem type can’t even be detected then your data is almost certainly irrevocably lost. This is unlikely to have taken place so we will ignore the possibility for now. If the kernel has somehow become undetectable / unbootable this is fixable. I will look into this and get back to you, unless you beat me to it. It will take me awhile as I have a lot of other things going on just now.