Hello folks! New face in town here with very interesting problem.

Not the PC freak myself, but I'm by no means "dumb" when it comes to IT hardware.

As stated above, I own Optiplex 780 and recently I upgraded it's q6600 processor with q9500 and everything works just fine. Then I decided to go for gpu upgrade and my friend had a spare GPU and without even thinking there might be some issues I just bought it  (very stupid of me, ik)

I currently run on 1gb ATI AMD Radeon R7 200 Series Saphire.

Card I bought is GeForce GTX 660 2gb Palit.

First thing I did was a mistake not to check it's required power supply. I ran it on existing 280W PSU and it restarted my PC several time and actually worked.

I tested it in Elder Scrolls Online and fps was around 90 BUT sometimes it would stutter a lot and during that period sound was also defective... like that slow motion noise or whatever.

When I saw that happening I turned PC off and after that I cant turn it on with GTX 660. I unplug it and plug older AMD R7 and it works fine.

First assumption - not enough power! I need bigger PSU. 

I tried with 300W, 500W and 550W and it didn't work. All mentioned PSU worked just fine with AMD R7.

After that I decide to check if, maybe somehow, I damaged GTX 660 with low power supply. I tested on 550W at my friend's place and it works just fine.

 

We both were stunned... had (still have ) no idea why it wont work with my OptiPlex 780.

 

After that I decided to look for professional help. There is company in my town which does the PC sales and repairs and I went to check the problem with them.

Their guy placed few months (alot newer card than both I own atm) old GPU into my PC with their MS PSU of 550W and it worked. After that he puts in GTX 660 and it doesn't work   We just looked at ourselves with that "how tf" look in our eyes.

GTX 660 WORKS, it's not faulty... yet it somehow just wont work in my Optiplex 780 after that first time it worked after few restarts. It doesn't even show the image on monitor like it does on other configurations. 

After that he assumed it might be BIOS issue. He told me he will flash my BIOS tomorrow and give me a call if it solves the problem. 

As you might assume, me being here means it didn't solve the problem and he thinks my motherboard isn't compatible with this GeForce GTX 660. 

I asked him how he explains the thing when it actually worked for like 1 hour at least.... he just shrugged 

Its really interesting issue and, if nothing else, I'd like to know definite answer on how and why it worked in the firstplace and now it works on every other PC and just won't work on mine?? 

 

Current specs i'm running as I'm writing this:

Operating System
Windows 10 Pro 64-bit
CPU
Intel Core 2 Quad Q9500 @ 2.83GHz 36 °C
Yorkfield 45nm Technology
RAM
8,00GB Dual-Channel DDR3 @ 531MHz (7-7-7-20)
Motherboard
Dell Inc. 0C27VV (CPU)
Graphics
Acer X193HQ (1366x768@60Hz)
1024MB ATI AMD Radeon R7 200 Series (Sapphire/PCPartner) 29