Hey there,
Recently whenever I start using the browser, loading sites like yahoo, etc my window/ tab responses lag severely. Moreover, there are some games that I play which doesn't even require graphics card. Sometime after starting these games a mild static interruption type of sound comes out of the speakers and the games lag pretty badly. At which point if I don't close (sometimes forcefully) the games the computer shuts down. During these events the CPU usage shows high usage and RAM usage shows more than 50%. I am saying about the RAM usage as I have disabled Aero and activated basic theme and changed the wall paper to a low colored one. When my RAM usage exceeds 50% my laptop starts lagging.
Some of these games require DirectX 9. Previously when I played some of these games they did not lag. I live in a tropical country. The weather is pretty hot most of the time of the year. The laptop used to get really hot when playing a game and the fan was fully running. So after a year I bought a cooling fan to help it cool down.
To solve the problem I updated all the possible software related to graphic including BIOS. It does not seem to make a difference. I ran hardware diagnostics and it showed this - 
The test are shown as passed, 
I also did the DELL hardware diagnostics and passed all the tests. Could it be because of the fan? I really can't figure out the problem and its bothering me.
BTW mine is a Dell inspiron N7110 with core i7 2nd generation, 8GB RAM and the Intel graphics card.