Hidden Program

I have a computer with a pop-up problem that is memory based instead of coming from the internet. It got on my computer somehow and it now starting to pop-up at annoyingly quick rates to the point where if I leave the PC for 5 minutes, it would overload the memory and cause the computer to reboot. I’ve done the virus scans and the anti-spyware scans with updated indices. However, they come up with nothing. I check to see if I can see it in the running processes window, but I see no new processes running. I believe that the pop-ups are being generated by a DLL that is somehow loading itslef and is using rundll.exe to run as an application. Please help.