COMPUTER FREEZE

When ever i do any things in my computer my computer freeze up. I have to re-boot the computer again to start. i can not use ctrl+alt + delete. I am using win 2000 professional. I checked event log for error log everytime it says:
The ptserial service failed to start due to the following errors

No serial device was successfully initialized. The serial driver will unload.

Please give me advice what does it means and what should i do? I am tired of re-booting my computer again and again!