What's happening is you are being bit by mains electricity. And this has happened (so far!!!!) under conditions where mains was not able to flow enough current to murder you.
Those conditions are subtle and quick to change. If there were higher humidity, if a neighbor turned on their dryer, any number of other things... that same shock could be fatal or maiming.
So I would stop pulling the dragon's tail if I were you!
Put it this way. "I need to use my PC, though" is less than "I need to not live in a wheelchair for the rest of my life". continuing using this as-is, is simply not an option.
There are two areas this can occur in. First, that power service may have a problem. That's easy to suspect in the old Eastern Bloc particularly, but it's not necessarily true. Contact your landlord and have him have it checked out.
Second, it can be your own equipment, especially if the equipment requires a ground connection and the socket is not grounded. Grounding is a safety shield, which is designed to catch wayward current. The problem is when equipment ground is not connected back to a competent ground back at the service panel and its equipotential bonding, it simply electrifies the grounded chassis of the equipment.
Worse, if several pieces of equipment are all plugged into a grounded power strip, and that isn't grounded to building, then you have what I call an "island of grounds" - so a ground fault on one piece of equipment will share the ground fault with all devices, electrifying all their chassis.
The usual culprit in PC equipment is cheap junk bought mail order, or smuggled in and sold at cheapie shops or flea markets ... in those cases, you're the importer - guess who is responsible for the item complying with CE safety standards! (the importer).
The first workaround is get a plug-in RCD. This will detect fault currents sufficient to kill you (like the one you've been feeling) and trip the power to your equipment to prevent that from happening. Consider this mandatory to even continue using the equipment. This will be a good time to not play your hardcore Diablo character :)
I would love to give you a diagnostic tree for chasing down this problem, however it's absolutely unacceptable to be touching the equipment to feel for a shock as a diagnostic method. Change conditions slightly and it becomes lethal - and the whole point of troubleshooting is to change conditions!
Try getting a €5 "non-contact voltage tester" and see if that will detect on the places you had been getting zapped.
Even so, be cautious of 2 pieces of equipment, one with a ground fault to neutral, the other with a ground fault to hot. Touching both at once can kill you, and the RCD wouldn't detect that. If you have reversible plugs, that situation could develop simply during unplugging and replugging things. The non-contact voltage tester will only detect ground faults to hot, so you might try flipping it and checking again.
If you have equipment with ground faults, get it fixed. If it's a PC, only the power supply needs to be replaced.
