Have you checked the windows event viewer?
Might be good to paste the error
here.
Also in case you are considering upgrading:
http://www.store.cakewalk.com/b2cus/category.aspx?categoryID=9 In general it is good to get up to a base system then resume further troubleshooting:
1) Update the chipset drivers and firmware of your motherboard. Google Intel driver update utility.
2) Update the display drivers of your display adapter from their third party site (what is the make and model?).
3) Update the firmware and driver of your audio interface (please supply details here).
4) Run windows update several times, and check the optional updates.
5) Make sure Sonar is on 8.5.3
6) Defrag.
7) After that check latencymon for further clues.
Also look out for per project crashes (i.e. plugin issues)...
Cheers...