Is it the graphics card or something else (LED diagnostic indicators)

Hello.

When I switched my Mac on this morning, it worked for a short while, then the screen displayed some small squiggly black lines all of a sudden. I could move the cursor for a few seconds after this, then everything crashed. I held the power button to power off and tried to switch back on. When I did, the same lines were on the screen and wouldn't boot properly. In a panic, I searched Google and tried a few forum suggestions. One solution was to hold cmd+ctrl+opt+A+V keys. I did this despite not having a clue what it was doing, there were just lots of other people who this worked for so I thought it'd be worth a shot. It didn't work and put my mac in a boot loop. It tries to load on the Apple logo and then I get a message: "Your computer restarted because of a problem. Press a key or wait...."

I suspect its the graphics card, so I opened my machine and took the graphic card out, cleaned some dust and placed it in a different PCIe slot. The same problem persisted. I removed the VGI screen connection from the port and powered on again. It didn't seem to restart this time although its difficult to tell without the screen.

After a little more research, someone I saw on YouTube suggested using the reset button on the logic board. I did this. Still nothing. I then used the button just behind the RAM to check the diagnostic LED indicators. This is the result:

When power is off:

SLP: Off

STBY: On - Yellow

ERRB: Off

ERRA: Off

OT B: Off

OT A: Off

GPU: Off

PWRG: Off

EFI: Off

When I switch on:

SLP: Off

STBY: On - Yellow

ERRB: Off

ERRA: Off

OT B: Off

OT A: Off

GPU: Off

PWRG: On - Green

EFI: Off

Anyone know what this means and could help me diagnose?

Please keep in mind that I had to temporarily remove the RAM to be able to actually get to the button and see the LED's. (I don't know if that has anything to do with the indicators or if it will affect the diagnostic result).

A couple more things you might need to know in order to help me here... About a week ago one of my RAM modules failed and I had to remove it and reconfigure my RAM setup.

Also, I saw someone on another forum suggest it might have something to do with the freezing weather - apparently this can cause the PSU to fail or something?

(3.1, early 2008 - all original specs except additional HD)

I'm a bit of a noob so apologies if this doesn't make sense. Hopefully its detailed enough!

Thanks in advance and merry Xmas :-) (y)