Can't open .exe files!! help please!

Hi, I need a lot of help, can somebody please help me here, this is what happened.  My brother recently got a bad virus on the computer that messed up everything.  Task manager was 'disabled by administrator' norton wouldnt run, everything was messed up.  My virus program was out of date, so i tried to uninstalled and install a new copy, the problem w/ this is that in the middle of uninstallation, the virus wouldnt allow it to fully uninstall, thus corrupting norton. 

 

My only solution was to remove the harddrive physically and put it on a second computer. I did this and scanned the HD for virus'.  After doing this, I found all the harmful files and fixed/deleted them.  After placing the HD back into the computer, I am able to boot again, but the problem is that no EXE files would run.  a message would come up saying 'cannot fine file (filename), please check that it exists.' All the files do exist, I dont know what happened.  The only way I am able to open certain files is to right-click and select 'run as..'  The problem now is that I am not able to run my current virus software because it is corrupt. 

 

My suggestion is to do a Repair Install of Windows XP.  I was directed to this link: http://michaelstevenstech.com/XPrepairinstall.htm   but after opening command prompt, I am suppose to delete the file 'undo_guimode.txt' but i cannot find this file... Is that a problem?  Is there still a way to do a Repair Install without loosing all of my data?

 

I believe the registry could be messed up, is there a program that could fix this?  I know that the computer is clean from any harmful files.  Also, when I run ad-aware, I scans the computer, but does not repair anything....

 

THANK YOU SO MUCH IN ADVANCE TO ANYBODY THAT CAN HELP ME, I GREATLY APPRECIATE IT!!!!!!!!!