Putting a Desktop Computer Back Together and Reparing it

This is a member of the public, not a business.

Problem: desktop computer powers up but does not send a signal to monitor, cpu and gpu fans are working. Connected the hdmi cable from laptop to monitor and monitor displays the laptop screen so everything there works. But once I connected the hdmi to the top section of the new desktop computer ''no hdmi signal''. I also tried connecting the hdmi cable to the gpu section of the desktop computer, still ''no hdmi signal''

I'm based in London, Chelsea. Project requires entry into the property to fix (not remote). I can pay up to £10 for travel costs.

Also, in trying to fix it myself I removed the GPU from the motherboard socket and now I can't put it back in. Job also requires the GPU be put back in place properly.

I have attached a picture of the GPU before I took it out (the correct placement).

If job only puts desktop computer back together I will be okay with that. Preference is to also fix problem though.