Hi, its troubleshooting time.
However, i find hard to believe a pc repair center did not find anything.. Were they out of stock of everything?
If its crashing during load, then its time to fire up some stress tests.
Do memtest86 for an extended period of time to see if it crashes. Then go after the GPU, try another one. A bios reset might be a good idea too to clean possible bad settings on ram timings.
If all comes clean, then it could be software, but thats more tricky.
You need to post more info about this, like temperatures and your full system specs.
Good luck
The Englishman