power supply - Can't screw PSU to computer case

As a software engineer willing to know more about hardware, I have started the dangerous quest of mounting my home computer myself.

The part I've been struggling the most so far is screwing things (like, literally), and after an hour working with the screws of death, I believe I have found hell on earth:

• My power supply is a Be Quiet! Power Zone (650W)
• I'm using a manual screwdriver (as I am not going to buy an electric one for mounting one single computer)
• The case is a Corsair 230T black (who'd have thought this was black?)
• The screws are the only available in the PSU box, which makes the choice rather easy
• I've tried with screws from the case package, and I really don't want to talk about this failure
• I thought if I manage to insert one properly, the other would be easy. Nope. Out of pure luck, I eventually managed to screw the top-left one properly and yet am still struggling with the others.
• It seems the screws need to be 100% precisely inserted, or they will no go further than 2 (what am I saying, it's even 1) turn with the screwdriver.
• I'm thinking the screws don't go further because they're not exactly centered (just a tiny bit to the left or to the right...)

Needless to say, the power supply is not moving in the case any more and I'm very tempted to leave it as is though that doesn't sound like a terribly good idea.

Any advice?

I would suggest the following:

Take the PSU out again, so the case is not in the way. Try to get the screws into the holes in the PSU by hand, if they fit and the thread is ok, that should go smoothly. If the thread is badly made or slightly damaged by your workings, you might encounter a bit of resistance but not much at that diameter. Maybe overcome that with the careful help of a screwdriver, but make sure you are actually doing good (right alignment, right size). You would be basically "recutting" parts of the thread so they match up with the rest. If it doesn't feel right, cancel it. Dismiss the screws and see below.

If the screws really only go in a tiny bit like in your picture, you most likely have the wrong screws (too big or wrong threading) for some reason. If you can, try different ones, maybe your case came with a bag of spares (kinda likely).

Once you know you have the correct screws, use them to screw that PSU (into your case). ;-)

bonne chance, good luck