Very poor performance on GTX460, clock speed constantly high?
Try to see if there is perhaps an altcoin/bitcoin miner running on your computer. If it is, it'll not draw much CPU, but it will propbably try to max out your GPU. Modern bitcoin derivatives are mined with algorithms (e.g. scrypt) that run on graphics cards instead of CPU.
Miner programs are generally identifiable by a very long 'command'/'parameters' string in the taskmanager in windows. CUDAMiner might be the name of a miner that is used on NVidia cards.