Aye, most prebuilt computers were not built with intentions of 24/7 max usage specially if you added a video card. I would sugest any cruncher to download temp software to monitor how things are going to avoid burning up there computers.
For GPU
Afterburner http://event.msi.com/vga/afterburner/download.htm
GPUZ http://www.techpowerup.com/gpuz/
For CPU
RealTemp (has an alarm for max temps) http://www.techpowerup.com/realtemp/
For CPU & GPU & Motherboard
CPUID HWMonitor http://www.cpuid.com/softwares/hwmonitor.html
There are others but these are the main ones i personaly use.