Blue Screen Error in Laptop?

I am using a Compaq CQ40 on Windows Vista with 4GB Ram, 320GB SATA HDD and onboard graphics.

Since a week, I am being faced with a lot of problems while booting. It either shows a blue screen error, reboots or freezes in between the boot. Takes me 5–10 minutes of constant tries to get it booted up. Even when if i manage to do that, it crashes or show a blue screen error and switches off while i work with it.

At times the laptop does not respond apart from the Caps and Scroll lock leds to blink continuously at the same time.

Please help me out, I am fed up trying to figure this out.