try going to start/run/type sfc and press enter. run the system file checker to look for altered or corrupt files
It may also be something being loaded from msconfig, go to start/run/type msconfig and press enter, go to the startup tab, this is a list of everything that windows loads at startup.
Uncheck anything you don't think is needed.
If your not sure go to start/run/type msinfo32 and press enter, go to left hand frame, software environment tab, expand it, select startup programs, you should see a list of the programs in the right hand column, go to the edit menu, choose select all, back to edit menu, choose copy, then paste the list back into this thread and maybe someone will notice something loading that could be the cause of the problem.