XPS l502x responding very slowly

Hello, i have Dell XPS l502x (bought it in november 2011) with intel core i5 2430m, 6 GB RAM, nvidia geforce gt540m 2GB and 750 GB Hard disk.

I have 2 operating systems on it, Windows 7 home premium 64 bit and Backtrack 5 (linux, 64 bit,  2.6.39) - using grub2 for multiboot

It is awesome laptop, but sometimes (rarely, mostly after running > 5 hours) Windows 7 stops responding, when i click on start menu, nothing happens, ctrl alt delete does nothing too, and hard disk activity led is constantly flashing, even after reboot it is like this, sometimes even grub2 doesnt start, boots into grub rescue...

when i leave it turned off for about a hour, it works again.

I have updated my bios to A07 (also tried reformating hard disk, removing all partitions...) 

Does anyone else have this problem?

Thanks for help