Hello! After many years of assembling and tweaking my own computers I've now run into a situation that I think I need all of our assembled expertise to solve. To start with, this is the specs at the start of all this (when it was working properly): Processor: Intel Core i5 2300 Processorcooler: Some noname cooler, Similar to the intel boxed one but with a taller heatsink Motherboard: ASUS P8H67-I Memory: 2x 4 GB Corsair Value 1333 MHz GPU: Palit GTX 460 PSU: Silverstone SG05-450 Other components: None The above system was starting to feel a bit dated so thought it was time to upgrade so I got myself a VTX3D Radeon HD 7950 X-Edition - 3 GB GDDR5. I was kind of disappointed with the small performance boost I got from it so figured it must be the CPU that was the bottleneck. In for a penny, in for a pound so i found myself a nice, used i5 3750k on line and thought that would solve all the performance issues... It all started to go wrong after i had installed the CPU and turned on the power. The only thing that happened was that all the fans would spin up for about two seconds then slow down to a stop and then do the same thing a few seconds later. It didn't matter if I had anything connected or just had CPU, Mobo, Ram & PSU hooked up. At first i thought the CPU was broken but that felt wrong since I've never run into a processor that just dies like that. When i was about to replace the new CPU with the old to see if I had managed to fry the board with static electricity of something I noticed 3 bent pins in the processor socket. I figured that must be the problem so very carefully bent them back and tried both processors. The old one worked just fine but the new one failed the same way. As usual when troubleshooting it's good to have redundant components so I when out and bought a new 1155 motherboard (Gigabyte GA-Z77M-D3H). At first i got the same problem (fans spin up, stop , repeat) but i noticed that if i used the internal graphics the computer would boot just fine. Since my PSU is on the weedy end of things i figured the old motherboard had compatibility issues with the CPU and that the new one just suffered power issues. Again convinced i had found the problem I went out and purchased a new PSU (EVGA SuperNOVA NEX750G Gold Power) but got the exact same behaviour as i had with the old PSU. The next thing I tried was replacing the new 7950 with the old GTX 460 and that booted up just fine on the new motherboard using the new processor. So to summarize: Old motherboard + old processor + either GPU: Boots up Old motherboard + new processor + either gpu/no gpu: Doesn't boot up. New motherboard + new processor + internal/old GPU: Boots up New motherboard + new processor + new GPU: Doesn't boot up. As far as I can tell it feels like there is either some weird incompatibility issue between CPU/GPU/Motherboard or it's a combination of my old PSU being too weak and my new one being faulty and not delivering the 750w it's supposed to. Both of these seem rather far fetched but this is an issue that really shouldn't be happening in this age of standardization so i don't really know what else it could be. Anyone else have any idea?