Since you didn't say what version of Windows you're running, I'm not going to be as specific as I'd like to be, but click the Start button and look in the upper right corner of the start menu to see if it has your user name there. If something happens to corrupt the files associated with your ID, windows can assign a temporary ID with the results you're reporting. If this is the case, you can create a new ID and copy the undamaged files and shortcuts from the old one. I'd normally give specifics, but since I don't know what version of Windows you have, I'm unable to do that here.
Yesterday, while using my desktop computer, I exited out of an application I was using, and then all of a sudden my desktop background went to the default Windows setting, and I went from having various PDF files, and shortcuts on my desktop, to just having the recycle bin and internet explorer icons left on my desktop.
My computer hasn't reverted back to factory settings because when I search, I still have programs such as PC Tools Spyware, Mozilla Firefox, iTunes, etc., listed in program files. However, for example, when I tried accessing Mozilla, it was like using it for the first time; it didn't have any of my bookmarks, etc.
I've run my PC Tools Spyware tool on the computer, and it hasn't found any malware, etc. So, at this point, I'm looking for advice/input now from some experts to help me. Don't know if RAM on my computer needs to be replaced, etc.
Thanks in advance.