Dell Inspiron 3847 performance speed slowed after GTX 960 installation

Jun 29, 2016
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I just installed a ASUS Strix 960 4gb OC in my i5 8GB Dell Inspiron 3847 with Windows 10. It's strangely slowed down it's booting and browsing speed. The PSU is a Seasonic G-Series 550w. What would you think would be causing the issues? I downloaded the drivers from Nvidia's website like recommended (driver version 368.81). I haven't had any crashes and games can run.
Average temps for GPU are 30-40c Idle, 50-65c running a game (mostly Overwatch an Medium).
CPU is 30-35c Idle, 40-55c during a game.
HDD is 38c, and MoBo is 28c.
All these temps are normal from what I read, so I feel the drivers might be at fault. I didn't mess with BIOs before installing it, the onboard graphics was disabled automatically. Or maybe the ram, should I get 16gb ddr3 for it? I've also been hearing clicking noise from the pc, most likely the hdd.
Also, what fan size is the Inspiron's stock exhaust fan? I want to replace it with an aftermarket one.