Could be a Virus/spyware causing this. If you find out the name of the process draining all of your resources, enter it's name into this handy website.
Has helped me understand what has been causing any of my sudden CPU 'draining'.
could be an incorrect driver installed for your chipset make sure your usng the manufactures drivers for all hardware not microsofts drivers! It is very unlikely to be a virus if its a clean install, on the other hand it could be a hardware fault!