I noticed this problem just yesterday when I downloaded the Torchlight 2 demo from Steam and started playing it on max settings.
Lo and behold, I only got 13fps while playing the game Which is weird because I'm able to hit ~25fps playing Crysis 2 on max (a game with much higher sysytem requirements)
After more observation since then, I've noticed that my laptop in general has slowed down a bit --- the mouse movement isn't as smooth, apps don't load as fast, and the system in general doesn't respond as quick as before.
So finally, I decided to benchmark my system again running Crysis 2 on max. Luckily, I benchmarked it two weeks ago using Fraps and got this result on max settings:
Download and use GPU-Z to check Core Clock as your drivers may be down-clocking or restricting your core clock and this would drastically reduce performance and if this is actually happening update your drivers but if you have the latest try reinstalling the drivers.
rgd1101 might be on to something there. If your system temps come up fine and there are no infections check to make sure the bios is set to using nvidia as default as some games might be having trouble choosing via software.
Could it be you've enabled hd4000 in the bios and not thinking it would be an issue lastdodobird?
Good news: I did a System Restore to three days ago and things went back to normal.
Bad news: I still don't know what caused it in the first place.
The affected programs listed before I did the System Restore were the following:
Adobe Flash Player 11
Torchlight 2 Demo
Saints Row: The Third
Magicka 2 Demo
a bunch of DirectX upgrades/installs
After the System Restore, I re-installed and played the Torchlight 2 Demo and was hitting 30fps on it minimum. That's a far cry from the 13fps which I was previously getting, so I've ruled out TL2 as the problem.
Right now, I suspect that either it has something to do with Adobe Flash or Direct X... but I'm thinking it's probably something that went wrong with Flash because before the System Restore, I was also getting sporadic ActiveX/Flash plugin errors while browsing that I didn't get before.