Reinstalling Ubuntu 12.0.4/Error no such device..Grub rescue

After using my laptop for more than 6 years, a Dell Inspiron 6400 (60Gb HDD, Intel Centrino Duo) it became rather sluggish and slow, sometimes with error messages that caused the OS to shut down, I choose to reinstall WIN XP that came with it, on a reinstall CD that followed the purchase of the PC, meaning a new clean install by deleting the whole HDD (all the partitions) and creating a new one.

But the reinstall of the same OS as before did not work out so well with many hardware-connected faults, so I choose to use my Linux/Ubuntu 12.0.4 LTS, startup creator on a USB to make a new clean install of UBUNTU OS.

Here I choose the 3rd option of installing the OS on a new formatted partion, by deleting the old one and not by manually making specific choices.

The install process went well, but at the end something happened.

The install process hang up and I tried to resolve the problem, but without success.

So, then I made a new reinstall again of the old WIN XP OS, by deleting/creating a new formatted partion.

It all went well.

I had again an error-ridden WIN-based OS, though basically working, but now I tried again to use the same LINUX/UBUNTU startup-creator to reinstall this OS, but now I cannot use the USB-pegg to do this.

By starting up the PC by USB interface as the first choice I just get the message: Error: no such device: f82.....Grub rescue...

How can I proceed installing UBUNTU on my DELL PC?

I am a Linux beginner, so please keep it simple, if there is an answer./Mikael