Why do games run slow on my pc?

[Alex]

I have a Toshiba A505-S6969
Specs:
Intel Core 2 Duo T6500 2.10 ghz
4 Gigs Ram
ATI Mobility Radeon HD 4600 Series Video Card (System Requirements Lab says it has 2.7 gb of video ram)

I just did a registry defragment, a registry error checking scan, a regular defrag, a virus scan, i deleted programs, i removed temp files, i turned all the visual options off, i ran disk cleanup, and ccleaner, ive ran error checking, ive updated my drivers, and removed the icons from my desktop.

I should be able to run a majority of games just fine. (Lego star wars for example) but everytime i play a game it usually starts fine, then after a minute or so it starts to lag.

I have done EVERYTHING that is supposed to make my pc run faster, and none of it helps.

PLEASE HELP ME!

 

[TehShet]

a 2.1ghz Processor is not Enough, Especially on a Laptop.. Overclock it if Its safe.

Games Requires to Run Smooth at least 2.6 ghz

as for The Ram and The Video Card, both are Good.