Problems with graphic on HP dv6703tx

Frankly, I dont know whether its a hardware or software problem. One day I was playing game on my HP dv6703tx laptop(os Vista HP) and suddenly the screen started to blink..then it restarted. But it won't boot successfully into Vista. I restored into factory settings but it won't work at all, after showing the windows logo it simply went hanged. So i installed win7, it goes all fine but the laptop nvidia8400MGS card wont work automatically. And aero things wasn't working too.so I have to remain happy with usual basic themes. I downloaded the graphic driver from HP site...and installed it in Win Vista compatibility mode. After restarting it seemed to work all right .I can re-enable the Aero things but then again screen started to go blinking after restarting it got stuck with the Windows 7 Logo.
...:::Please Please please Help me out::::....

Have you noticed when playing your game, that the laptop is hotter than usual. What it sounds like to me, I'm just guessing here, is that under normal usage your are fine but when you go gaming is when you have your issue and that it is over heating. This is why I asked about the heat of the laptop.
First thing I would rule out is an over heating issue; use a laptop chiller, you can get one at walmart for $20. Next; get a can of compressed air and blow out all your ports (usb, audio) and intake/exhaust ports. Blow your laptop out on a regular basis (bi-weekly or monthly). Once you do this, then play you game and see if your problem reoccurs. Then I would recommend checking your system for malware, adware, spyware and virus's, also check your systems registry for errors and defrag your hard drive for system performance. Here are some suggestions for you.

Adaware
Spybot S&D
Ccleaner
Auslogics disc defrager
Auslogics registry defrager
Malwarebytes
Revo uninstaller
Tuneup Utilities {2009 for Vista} and{ 2010 for 7}: (paid subscription)

All these are free to download except for Tuneup Utilities