Yikes!!! 77C is within specs, but barely... yes, but from a preactical standpint, that's barely. Especially after just a 5 minute warm up. The heat bleeds over onto the video RAM and makes it go nuts!
As far as what the temp lead looks like? Well, in my Thermaltake case, it is a black, rectangular thingy with two wires coming out of it. Ewe! Ick, a mini case! Oh well, and there's half of it! Still, with two 120 mm fans, you should be ok. So what's the case temp read after one hour of full load running of the PC?
And your power strip or whatever is how old?
And your wall outlet is in what shape?
I'm trying to save you from a power supply upgrade, but you ain't makin' this easy!