Have an issue where a PC is powered on, but no signal to the monitor. Problem is not consistent though – after unplugging the power cord for a while, sometimes it works.

Specs. are a 2014/15 Pentium G, 4GB DDR 3, Asus H81 mobo, Corsair 430 watt PSU.

• Troubleshooting so far – checked seating of all cables and RAM.
• Tried swapping RAM to different slot
• Power cycled

During this trouble shooting it also went through two other ‘phases’ – upon hitting the power switch the cpu fan would spin for a second and then nothing, then spin again for a second – like it was in a cycle (with a little clicking noise). Then after further checking of cables and such, there was no power at all – dead as a Dodo! So, I decided to check the PSU. Used a couple of YouTube tutorials, and I think I did everything correctly – paperclip connecting green and black – PSU fan spun. Then went on to test 12 v, 3 v, 5 v and the (I think it was called) the ‘reverse 12 v’. Things to note here, if I did it correctly – when testing the 12 volt and 5 volt using a molex connector, I got the 5 v, no problem, but the 12 v test gave me -1.56 v. The reverse 12 v test gave me about -10.96 v.

So, after all that, I put her back together and gave it one last boot up, and…it worked straight away. I ran some tests on the HDD to check its health (fine) and made sure Windows updates had been done recently, plus saw the user (an older lady who uses the PC for basic browsing) had anti-virus running, which she didoes, so I wasn’t too concerned there. Then, powered it down, left it for half an hour, booted again…no signal, back to square one.

Only other thing maybe worth mentioning was that the user had a power cut recently, possibly when the PC was on – maybe that caused an issue?

TL;DR – If I did the PSU test correctly, could getting -1.5 v for the 12v test be an issue causing intermittent ‘no signal’ when booting up a PC?

Any advice greatly received!