Hi! My Mac Pro 5,1 Mid 2010 has been running fairly well recently, apart from an issue where I cannot seem to get it to upgrade past OS X 10.13.4, Boot ROM version MP51.0089.B00, over the last few months. But the other day, after I powered it up and was on it for about five minutes, the screen suddenly went grey with thin white lines running horizontally across it, then it powered itself down after about 30 seconds and immediately tried to power itself on again, only this time unsuccessfully with a black screen and the sound of the start up chime every five seconds (the chime was very faint, barely audible above the sound of the fans). I shut it down and tried a PRAM and SWC reset but to no avail. I also noticed that no power was coming from the rear USBs, and a keyboard plugged into the front USBs I believe was also not recognized as I tried to do a SHIFT restart, which also didn't work. I then tried to follow the diagnostics from this thread: https://forums.macrumors.com/threads/mac-pro-5-1-no-boot-up-black-screen.2124447/ Inside the Mac, there were no LEDs lit up, all the fans seemed to be running, and the little white light on the outside start button was on (all the while the chime would continuously sound every 5 secs). Upon pressing the LED Diagnostic button, I have the PWROK (green), 5V STBY (amber), SYS.PG (green), and GPU OK (green). The red light on the left of the processor flashes once for a millisecond upon startup, as does the LEDs for OVTMP CPUA and OVTMP CPUB briefly flash red when connecting the AC power cord (I'm assuming both LEDs as I only see a quick glow of red since they are partially hidden by hard drive bay 1). The monitor I doubled checked hooked up to another source and it works fine. I have a fairly new SSD as the boot drive and a HDD to store everything else, both changed about a year ago. The RAM was upgraded a few years after buying the Mac. The ATI Radeon HD 5770 1024 MB is original. Thanks for reading, and for any assistance you can provide!