Prime 95 is baking CPU
you first has to find a fan control to turn off fan without opening the case. Then run Furmark to toast the GPU, at the same time run Prime95 to toast your CPU.
Maybe it won't work, as modern chips has internal sensor to turn off when reaching certain temp. Also after certain temp the CPU will crash so you can't finish the job.
But doing so will surely shorten the lifespan. :)