[troubleshooting] display and peripheral devices start going crazy

so this is my old pc: i5 3470 8gb ram 1333mhz MSI GTX 260 motherboard: asus h61m-e and stuff connected to the motherboard starts going crazy once the cpu reaches 37 degrees. the screen starts flickering, the mouse and keyboard go crazy turning on and off and so on. so I already tested the psu, it's not it but I'm sure it's either cpu or motherboard. has anybody had this issue? and if yes, how did you solve it?