dont worry about the svchost.exe its typical to have multiples of it, and you never said how much ram your using, befor you get into any complex solutions have you run a boot time antivirus check,...

first i when its idle how much ram and cpu power does task manager say? secondly have you tryed all the basics? disk defrag, chkdisk, virus scanner and spyware removal?, personally id say its a virus...

you may be having a graphics card error, as you navigate with windows you may not be dumping your cards cach, as a result after a while it fills up and crashes, try updating its driver, post if it...