xps 8300 won't start up, green LED on psu is lit, amber LED on mobo is lit

Hi,

I have an XPS 8300 (about 6 or 7 years old) and I recently bought a new GPU (Radeon RX 550) for because the integrated one isn't so great. It only requires 450w which is 10w less than the stock 460w PSU so I didn't think it'd be an issue. The PC detected the video card just fine and started up. I did not make any changes to the BIOS.

The PC ran for about a month until one day, I put it to sleep. It went to sleep just fine but when I hit the space bar to boot it up again, it did not boot. It continually attempted to because I can hear all the fans starting, but then it would stop and try again. The power light was blinking amber during this process and the MOBO lit up amber as well. I tried to hold down the power button to manual reset, nothing happened. I had to wait until it powered off from a failed attempt to boot and then I unplugged the power cord.

I reset all my hardware components, held down the power button for 10 seconds w/o anything plugged in to rid of any residual power and still no luck. Now, I have plugged everything back in and tried to power up and it doesn't work. Fans would start and then stop immediately. The power light doesn't light up at all. It doesn't even stay on long enough for me to get a feed to the monitor. There is still a green LED on the back of the power supply.

Any suggestions? is it the PSU? is it the MOBO? Please, let me know what you think so i can buy the proper parts.

Service Tag:  

Thanks,

Tim