ya.... the stock hsf scared the crap outta me too.. now i'm happily running a scythe ninja... i suggest you too get an aftermarket heatsink so you can escape these fears!
unless that mobo has power saving on in the BIOS so the fan will stop and start leave your case off and watch the CPU fan see how it goes. Also go into the fan settings in the BIOS and turn off any fan control and put it on full.
well ive turned all the fans on full, and sometimes the temp would go down to 51-54C and then at one point it was at 64C with a couple of programs up while playing BF2142.