user profile suddely not recognized and so I can't d/l new version of a regular prog

I have a windows xpsp2 profile and all of a sudden have had a mega problem in that I can't d/l a version of a purchased program.
I have myself been trying to figure it out on my own since July, uninstalling the last version that worked and doing a reg clean and then a reinstall. However that simply would not work.
I did this in regular mode and safe mode networking in order to get the setup off the program site. Still no luck.

I finally decided to take it to a trusted software tech who has worked off and on for glitches in my family's notebooks when we can't fix them.
He checked it out for malware, which I had done as well and it was clean. I do daily checks for updates and daly scans.

Then he checked other areas for errors and made some changes and still the same thing.

So he decided to change the User name to his own name with a New password as he noticed an error in area that he was checking.

He did the d/l overtop and it worked.

Then we tried after a Reboot to do it under my user name and password and it would not work.

He kept my computer and said that my user profile was corrupted????
I don't used this notebook much and am wondering what caused this to suddenly happen when no malware was found in the registry?

Does anyone have any ideas.
Could someone have been trying to get into the notebook and screwed it up? I have a Bios password and also of course a Login password.

Now apparently the User profile has to be fixed and since I don't want this to happen again I am looking for the possible cause.
Thankyou for your time.