Computer gurus - crashing PC

[ginge191]

Built this PC about 2 years ago and never had a problem until now.

Various problems:

 - PC will disconnect monitor/display but continue running in the background
 - PC will attempt to boot for 2 seconds, turn off and repeat
 - PC will freeze on screen when multiple processes are happening - ie, loading 2/3 items of software at once

All problems when reading around point to PSU.. 

specs as current are :

Windows 10
intel i5 4460
4GB RAM - corsair vengence
PSU - Corsair CX500M
Mobo gigabyte GA Z97P - D3
Radeon R9 290x

Ideas on a postcard...

EDIT:

It also went through a spout of throwing up srttrail.txt a few times - BIOS resets seems to sort this and the above issues out...MOST of the time but it's so unpredictable... could be running the PC for 2 minutes then boom, dead, or 2hours...