Ana,
I have seen this before and this isn't something that happens to just IdeaPads, it can happen to any Windows XP computer. That fact it happened on your IdeaPad is just unlucky.
What happened (for whatever reason) is your Windows user account became corrupt and Windows was unable to load that profile. It then either loaded a Guest account or some other account stored on the computer.
This could happen for a number of reasons including a failing hard disk, but 8 times out of 10 it's caused by some type of virus/malware infection that corrupts parts of the disk. None of your data is probably lost. Windows stores user account information (including files in the "My Docs, My Pics, etc") in the following directory, so if you navigate here via "My Computer" you can move your data to other parts of the drive or someplace else, the location is: C:/Documents & Settings/<your old user account name>/
Once you get there, look through the folders for your files and move them.
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After the files are safe, go ahead and create a new user account via "Control Panel/Users". Once you've created another account, restart and boot into the account you created.
At this point, I would scan the computer for any infections (I prefer Avira Anti-Virus and Malwarebytes) -which are both free, and clean them up.
After the computer is cleaned, move your files back to the user account you just created and delete the old one.
You may also want to try going to "Start" -> "Run" and typing "scf /scannow" (without quotes) to restore any damaged Windows XP files.
What you're essentially doing is deleting the corrupt account, creating a new one, moving your data from the old account to the new one and checking for any infections. After your data is safe, you could just skip what I said and not bother to try and clean up Windows and just restore it to factory settings if you want but I find too many people suggesting "restoring" over trying to diagnose/fix the actual problem but it's up to you.
You can also try running "chkdsk /f" (no quotes) in the Command Prompt and following the directions.
Good luck
It must be a hardware glitch. If it happens again I think I will be contacting Lenovo. I could have spent quite a bit less on a different machine and not had this problem.
