Freezing up

A few things to try.

Check the event logs on your PC for Hard drive errors. If the lockups are random they could be caused by bad blocks on your drive in a paging or system file. If you see disk errors, replace the drive immediately and make sure to keep proper backups.

Next, update all drivers, especially the video driver. Often lockups will be caused by Video driver corruption. Dont be scared to install beta versions of drivers for your laptop in an attempt to resolve the problem.

Next, search out a utility boot CD from the internet. There are several, usually running linux but most contain a memory test utility that you want to run for a long period of time (several hours) to see if after a stress period you start getting memory errors.

Next, search for speedfan on google and install it to monitor the temperature on your processor, this problem could be caused by dust buildup on the processor heat sync or cooling fan. Generally it would take some time to have this problem lock up the system, however, after the first lock up and reboot subsequent lockups would happen more quickly.

Many laptop repair depots will do a service for under $100 where they will dissassemble the machine, clean the heat sink and fan (or replace it) and apply new thermal grease.