It all seems very strange but today when I turned on the computer a completely different screen came up, with the windows desktop and all of my items saved on the desktop were gone. When I tried to open Firefox it was as if it was the first time I had used it asking if I wanted import bookmarks. I was also asked in a prompt if I wanted to take the windows tour. /
It sounds like a temporary profile was assigned to you when you first logged on and your normal profile was assigned the second time. This happens when Windows cannot read your real profile for some reason such as file system corruption or disk read failure.
I would run a chkdsk /r after booting to the recovery console with a Windows XP CD, run it repeatedly until it finds no errors (it is likley to take hours each time). If you don't have an XP CD let us know and we will tell you how to burn a disk that will let you. Contributor ElderL has loads of posts about chkdsk /r if you want to search for one of them.
Tricky