Brand new 64 bit rig, 16 gigs of Ram built by an audio computer company. All the latest drivers, updates etc. I am running one instance of Superior drummer and 5 instances of Peavey Revalver. Sonar will lock up if I press stop during recording. I have to end the program to get out of it through task manager. Ends up rebooting the whole machine. Doesn't seem like I am asking it to do a lot? What should I look for?

What is your audio interface? Are you using it in ASIO mode?

16GB of RAM is a lot. You might have a bad chip. Run the Windows 7 memory check or memtest. 

Does it lock up when you're not using those two plug-ins?

I will run the test, but like I said this computer was professionally built by a company that makes DAW computers. All I have running are those plug in's, it probably would not crash with nothing going.

Well I froze superior drummer and so far so good. Maybe my settings are a bit too low for all that stuff. I am running ASIO at 64 samples.

That's probably too low. What soundcard? 

That 5 instances of Revalver sounds like a lot to me, especially with latency set that low.
The 16 gigas of RAM doesn't help a lot with them, or does it? I've always assumed the amp sims tax CPU, and do not benefit much from added RAM.