Why is my ps3 slim doesn't show red light?

Hello, I hope you’re doing well.

I wanted to ask for some advice about my PlayStation 3 Slim (model CECH-3003B) that stopped powering on. I just want your professional opinion or chance estimation about what could be wrong.

Here’s the full history:

The console worked fine from 2011 until 2021.

One day while playing Midnight Club 3 Remix PSN Classic, it froze completely. I couldn’t shut it down normally, so I unplugged the AC cable.

It still worked afterward but froze often and had low FPS.

In 2024, I opened it, cleaned it, and replaced the thermal paste (Corsair TM30). Some screws were missing, and I think the motherboard wasn’t fully seated.

After reassembling, it no longer shows the red standby light. No power at all.

The AC power socket feels loose now, and when I move the AC cable, I sometimes hear a brief buzzing sound from the PSU socket area.

The console was once opened on a carpet, and I used a vacuum to clean the motherboard and PSU vents.

The PSU is an APS-270, and the model region is PAL.

I haven’t plugged it in recently; it’s currently stored safely until I can get it checked by a shop.

Could you please tell me, based on this information:

What are the most probable causes?

What’s the chance that the motherboard is still alive?

What components should I ask a technician to test first?

I’d really appreciate your honest opinion — I just want to understand what likely went wrong before I take it in for repair.