Hello there, xZinou.
There's a couple of things you can try:
1) don't overclock a laptop's video card, and specially a 8400M GS.
2) install latest drivers for your card (260.99)
3) don't force vsync on on the control panel, unless you're experience screen flickers, if you don't, then manage vsync individually on the application/game/program you're using.
Try those and report back, please
EDIT: after you uninstall your current drivers, please run Driver Sweeper to delete leftovers from the previous installation, that will decrease the possibility of having an issue when installing newer drivers!