What was done to this computer just before this problem started occurring?
Look at new Software or Hardware being added and also remember Windows Patches, any of these could have caused this problem to happen.
For a cure you can try using the Trial Version of Iolo's System Mechanic available from here
http://tinyurl.com/2e93vb
If you are only looking at the Trial Version do not download the Professional Version as the only difference between that and the standard version is an AV Scanner which will be useless to you as a 30 day trial.
After you have this installed run the Repair Option and now see if the system works correctly. If it doesn't you will most likely need to do an Inplace install by following the directions here but remember with anything like this you should perform a full system Backup before going ahead with this procedure.
Also if you have Windows EFS in use remember to backup all your data without encryption or grab a copy of the Encryption Key. The instructions for an Inplace install are here
http://tinyurl.com/g4bv8
If you need to make a copy of the Encryption Key the instructions are here
http://tinyurl.com/3cd8hf
And just in case you need to Take Ownership Of the Data Files the instructions are here
http://tinyurl.com/3aw7
Col
