Ps3 not working after sending it to repair?

I opened my ps3 for a routine cleaning, which I do every 2 to 3 years. But this time, I accidentally ripped off the Fan connector on the motherboard. I replaced the thermal paste anyways, and reassembled it back. I turned it on to backup my files and savefiles, but I would only have a 3 minute windows, after which, the console would display a warning message, that it was overheating and therefore was going to shutdown as a preventive measure, which again, is normal considering that the fan was not connected. I monitored the Cpu and You temperature during the process, by pressing Start + Select everytime, it was rising gradually.

Now here's what happened, I sent it for repair, but when I had it back, it wasn't working like before : the fan was connected, but it was messing around. It would max out right away after I boot it, then slow down, then max out again, then slow down and then then turn off, I hear three beeps and there's red blinking. Then when I boot it again, no display, unless I let it sit for a couple minutes.

I wanted to see if it was overheating, but I can't even get to the Xmb sometimes as it would turn off. And I didn't want to open it. I called them, they said it's a Gpu overheating issues, and that there's nothing they can do. How? It never had any overheating issue or whatsoever! But they're trying to pin it on me, saying that I opened it because it was overheating but it was not ; it was a routine cleaning.