Strange mac pro no start

I hAve a 2008 mac pro, it ran fine up until about a year ago, one day it shut down and wouldn't power on, a few days go by and it powered on normally. A few months later it powered down and wouldn't power on, I tried a few things and eventually it powered on after no wanting to start for months. This time I left it on for a,on the straight when it powered off again. I haven't been able to get it to start. The ota and otb lights are red when power plugged I, I removed all memory and put only one module in, plugged in and the machine gave o lights, nothing, when I hit the led diag only a standby lit up. After a few minutes by itself it powers on, fans running full blast, red lights turn on and the disk drive tray opens after a few moments it turns off, then on, then off, then on, then off, nothing is displayed on the screen. Any ideas what this is?!?

Probably the power supply.

By the way. Most things work until they don't work.

- Nick

Agree with Nick's diagnosis. My Mac Pro 2.1, the model before your 3.1, was in storage in LA prior to being shipped home here to Australia and same problem. If you wish to try, get a second hand unit such as this or sell say for $350 as is:-

Apple 614 0400 980W API6PC01 PSU Power Supply for Mac Pro Early 2008 | eBay

And replacement:

https://www.ifixit.com/Guide/Mac+Pro+First+Generation+Power+Supply+Unit+Replacement/32222