I would upgrade to at least something more than 350w because some of these OEM machines are supposed to output 75w but are limited by the manufacturer to 55w so the card may not respond if it doesn't use external power. If this problem is true in your case then scrap the entire PC as no GPU will work with it even if you upgrade the PSU, the PCI-E is still limited. One suggestion from me is to try get a deal on one of those Optiplex Mini Tower machines. They have loads of potential for upgrades as is my one. I had bought an Optiplex 990 Mini Tower and upgraded it to it's max. It had already an i5 2500 @3.30Ghz and 8gb DDR3 memory. All I had to do was stick a Corsair VS550 (Silver Series not Gold) and a gigabyte RX 570 in there a boom I have a gaming PC.