Constantly reseting and and no picture.

i5 3570K 3.4GHZ 1155 soc.
ecs z77h2-a3, iz77 1155 soc.
r9 380 2gb ddr5 strix gaming
gskil ripjaws x series 1333mhz x2 4gb
600w b600 coolermaster v2.

At startup pc works one minute without a picture and restarts and constantly do that over and over again.
Providers and servicers told mi it's everything fine with my parts.. dunno what the problem is..

If the parts are all fine then it's the way they've been put together, or software, or firmware.

Has it ever worked? If so, when did it stop working? What changed?

Hmm. Try a Live OS (if you can) and see if the issue is even remotely hardware related.