GPU Overclocking Problems

While over clocking nvidia gpu's (gt 640 and gtx 650 ti boost) using precision x and afterburner after I put either the core clock or the memory clock past a certain point the clock speed for core and memory goes down to 324 and 324 on the gt 640, it works a bit differently on the 650ti boost but I do not have it with me at this time. And once that happens I cant seem to get it back up with out re-installing drivers which is not fun to do every 5 seconds while overclocking. I've tried many different driver versions to stop this with no avail. Temps are still in the 50's so not a problem with that.


If any one knows what might be going on please help.

If you've reached a point where the card is throttling the memory and core - its because you are pushing it too hard and its dropping back to prevent damage. 

Overclocking a 640 will do very little for performance - it has a small bus, ddr3 and a really low shader count and is really just a card that is on par or just a bit better than onboard gpu's. Is perfect for a HTPC or office machine but very little else.