Precision 5510 screen freezing/machine locking up.

My Precision 5510 is experiencing screen freezing/locking up issues not long after loading Windows, particularly when browsing the internet. The nature of the lockup is:

- keyboard backlight still responding
- display frozen on last view
- all keystrokes, key commands and windows key ignored
- mouse pad ignored (pointer motionless)
- ctrl:alt:del ignored

Does anybody know what might be causing this problem?