Should probably have put the thread in tech support but I will give you a few hints at things that might be wrong.

First is sins updated to 1.05?

Secondly do you have the latest drivers for your onboard video?

thirdly is your bios up to date?

fourthly have you updated chipset drivers to the latest versions?

Fifth make sure your onboard sound drivers are up to date.

Really the 1.05 update is most critical but you should make sure you hardware is fully up to date on its drivers. Once you have checked all those things and updated anything that needs to be try again. Let me know if it does it again there are other things to check but these are the general culprits a lot of the times.

That depends usually best to go there but sometimes its best to check the computer makers websites first since sometimes they have done things to the hardware that make the ati or nvidia drivers not run at peek efficiency if you are running the ones off of ati or nvidias site. This tends to be most visible with proprietary parts where you are stuck having to not be able to play at all due to the manufacturer not getting updated drivers out often, or playing at a slightly inferior capacity of what the hardware should be able to do by using the drivers that are not configured for your particular machine. Of course we are probably only talking a few frames a second but to some people it matters.