Figuring out which PC part is faulty

I have an odd scenario and I'm having trouble figuring out which is the faulty component.

First of all, the video doesn't work, monitor says it's not getting a signal. Monitor's not faulty (works on other computer) so the first suspect was video card.

However 2 things make me think it's not the video card. (Don't have another machine with PCIe around to test definitively) First, the GPU fan is spinning so it's getting power. Second, tried putting in an older PCI video card that is known to be working (pulled out of another working machine) and there's still no video.

Normally if it's not the video card I'd suspect the motherboard, but everything's getting power on the mobo, so I'm not sure. The case apparently doesn't have system speakers, so can't hear any of the diagnostic beeps either.

Also not sure whether a faulty CPU would cause no image at all either.

The parts are brand new so something's going to get RMA'd but I'm not sure which component is to blame in this case.

(Only slightly related, but I also accidentally put too much thermal paste on the CPU. The fan/heatsink instructions said to put the whole tube which seemed like a lot compared to previous experience, and as I started squeezing I knew it was definitely too much and stopped at about 1/3 but against my better judgement I didn't wipe any off. I'm not sure whether that would cause problems other than not cooling as effectively as it should)

Solution 1:

If the thermal paste you have used is something like Arctic Silver 5 then you may have some trouble if you have shorted some pins on the CPU or the motherboard with it.

Sounds like it could be a possibility if you have used too much. If so, you may be able to clean it up with some isopropyl contact cleaner. Hopefully the CPU/MB is not fubar and you will be lucky!

Quoted from the link above:

Not Electrically Conductive: Arctic Silver 5 was formulated to conduct heat, not electricity. (While much safer than electrically conductive silver and copper greases, Arctic Silver 5 should be kept away from electrical traces, pins, and leads. While it is not electrically conductive, the compound is very slightly capacitive and could potentially cause problems if it bridges two close-proximity electrical paths.)