Microstar MD2852 Overheating Problems

Question

Hi,
I have a microstar md2852 laptop which gets fiery hot very quickly. It has an upgraded 160gb harddrive + a new 1 gig memory card equalling 1.25gb total memory. I am not sure what the video memory is. My biggest problem is that within about 10 minutes tops it just freezes up. It did the same thing before the upgrade but took longer to freeze. If you could let me know what the possible causes could be I would be very grateful.
Thank you