|"nzxt phantom 410 with extra fans added to it"|
Ugly case but we all have our personal likes, I guess. The case doesn't need extra fans. One exhasut fan in the rear is all that's necessary. Depending on what you added & where, you may have actually lessened the cooling ability.
"randomly my computer goes to the desktop and stops responding"
Could be a software issue or infection. Which anti-virus program are you running? Could also be bad RAM. Have you ever run memtest86 for an extended period? Have you manually configured all the BIOS settings or are you simply running auto/defaults?
"could involve my Gpu overheating"
Post the GPU & CPU temps.
BTW, your PSU is NOT crap. Corsair markets some of the best PSUs available. And in case you didn't know, Corsair doesn't manufacturer PSUs. Your 650W is made by Channel Well or Seasonic.