Lockups are normally hardware related. I would start by removing and reseating RAM and then run memtest86.exe in the extended test mode; in case it's system related run chkdsk /f from a command prompt and type "y" about the reboot. Then run sfs /scannow to check system file integrity. Disk Cleanup and then Defrag.
Get a copy of hmonitor.exe and see if it will report the CPU temperature (it's not compatible with all laptops). If you see a rapid temperature excursion when running spybot, that's a good indicator of a cooling problem of some sort. For that matter, do a complete virus scan, and spybot/ad-aware scans.
Check your startup applications, msconfig from the run command, startup tab, and verify that everything that is starting is necessary. Go to this site for help in identifying what is starting. http://www.pacs-portal.co.uk/startup_content.php
You might also remove the video driver and any associated software, reboot and reinstall it using the latest driver from the Sony support site.
Not forgetting to open Device Manager and verify that there are no problem devices listed. Check Event Viewer logs to see if there are any repeating warnings or errors that might provide a clue.