it looks like i solved the problem myself

first i did try to find out if some of my hardware was damaged or broken. switched the rams, started pc with only 1 each, everything was fine, but the problem was still there.

then i downloaded 3 different anti malware/virus programs and let them take actions. it found several things, i guess this is normal because they want to sell their product, but it also fixed my problem

now it shows 16 gb of ram when i go in the control panel / system instead of 7,98.

i m not sure how this could happen. was there a harmful program that deactivates or blocks half my ram? what is the purpose of this?

i m happy that everything is fine now and the problem seems solved.