Hi,

Ive just tried my NES system for the first time in many many years. First it worked fine, but then after about 5 minutes, it just started blinking (on the red light beside powerbutton), and syncronized with this screen also blinking from black to grey. It just started out of the blue, without me touching anu cables or anything. Ive tried restarting it many times, and i dont know what else to do.

Anybody recognize this behaviour, and is there anything i can do to fix this?

Thansk.

Yep, your game / console needs cleaning.
Try this first, make sure the contacts on your game are spotless. Clean them vigorously with a q-tip and isopropyl alcohol. If you have a NES cleaning kit, use it. Alternatively, you can take your least valuable nes cartridge and slide it in and out of the connector about 10 times. if that still doesn't work, disassemble your console and clean the the connector more thoroughly. (some youtube videos have suggested boiling, but I can't vouch for it personally as I have never tried).