Vista - Memory Diagnostic Tool can't be killed

Memory Diagnostic Tool keeps launching on boot up

I had my ThinkPad T400, new, running just fine with one 2gb stick of memory. I added an identical stick that I pulled from another ThinkPad, but I guess they did not form a matched pair because I got the blue message that the new hardware I installed should be removed. I tried running the memory check but it would not finish and I could not remove it. I removed the extra memory and went back to the single stick that worked in the first place, but now I have a permanently running memory diagnostic that I can't get rid of! It never is able to finish, so it sits on my task bar when I bootup and I can't close it. Not sure how to stop.