Hi
Do you have a lot of files on the computer that you can't afford to lose?
If not check the Dell website for instructions on how to reset your computer.
The USB drive may be the recovery files?
If you do have things that you can't lose, then you'll have to look at someway to recover the data from your hard drive before restoring.
One way is to create a Ubuntu disk on another computer and use it to boot your computer and copy the files off of it.
More details would be helpful, i.e. computer model number, how many partitions etc.
Once it's running again you should make a System Image of your OS so that it can be quickly restored after a crash.
You should also partition your hard drive so that your important files aren't on...