Run some diagnostics test. Reset your BIOS Defaults (if possible). The Ultimate Boot CD has some great diagnostics tools. http://www.ultimatebootcd.com/
You should run a Memory test and some Hard drive test. Also Verify your hard drive is not making noises, i.e. Grinding, clicking, reving, or anything alike.
Go to start, right click My Computer and Select Properties. Click the Advanced Tab, under Startup and Recovery click the settings button, then under system failure, uncheck Automatic restart. Now if you get a Blue Screen of Death (BSoD) you will have time to look at it and write down the error codes and such.
You may also want to run diagnostics on the CPU registers, just to make sure the Processor is not the problem. If all those test pass, Call Compaq for their diagnostics utility and run a full scan on all hardware to test Motherboard, Hard drive, memory, CPU, Video, Audio, Network Cards (Including Bluetooth and Infared), and all other Adapters. See if anything fails.
In the event nothing fails Try a system restore in safe mode to a date before it started freezing. If it still fails, reimage (i.e. format and reload windows)
Thats a few Quick (quick meaning within a few hours) things you can try.