[SOLVED] Need help identifying electrical issue

[thisvpr]

Every few weeks my PC randomly starts blinking (power LED) klicking (fans starting) when its turned off (the power switch from power supply is on ofc)
It looks like it gets short time power every 0,5 secs. I can not start my PC meanwhile!
I always fixed it by opening and blowing in the case. (there isnt much dust, but it helps).
The air input from my power supply is not from inside the PC (-> im not blowing in it for the fix) . My first guess is a problem with the power supply but it doenst seem like it.

Any ideas how i can identify the problem?

 

[william p]

Do you have a UPS (battery backup installed)? The batteries in those get old. Many of them can be replaced, many others can't. If it's replaceable there is usually a removeable cover for doing so. The old battery is often swollen amd hard to get out. Be careful using tools. if you crack the plastic case acid will come out and destroy anything it touches, including you. Good ones will have an alarm when going into backup mode. Cheap ones just a light.
Rubber gloves, goggles and some baking soda solution are good to have around when doing this.