Pc froze now no signal to monitor

Hello

Last night i upgraded my pcs GPU and PSU (asus strix geforce 960 and a 550w corsair bronze rated psu). All worked fine for about a day then my pc just froze completely (sound and everything) and when i try to reboot i get no signal to my monitor. Both the psu and gpu are brand new so do i just need a more powerful psu? I have a 2009 3.4ghz i7 which i hear can be quite power demanding, or maybe my ram is just needing updated too? Im in a pickle with this and would apprieciate any help !