My fcomputer fun is running and after some seconds it stop and restart again ?

There can be many reasons for this to happen such as failed hardware (power supply or memory) but one of the most common which occurs out of the blue is over heating CPU from a dirty fan and heat sink not cooling it properly. This will usually occur along with a few beeps to tell you that the CPU is getting too hot. If your Heat sink is plugged with dust and hair you will need to unplug from the wall and get in there to clean it up. Canned air can help but for really badly plugged sinks, I always remove the fan screws and fan assembly and clean the fins with a soft cheap paint brush followed by canned air to get all the dust out of the box as well. It's a good idea to do a basic cleaning of your fans and board while your in there just be sure to touch some metal to eliminate any static charge. If your CPU's thermal paste is dried out it can also cause over heating but it's a little more complicated to clean the old off and put new on so taking it in to a tech if your not brave may be a better option.

As for static charges they do make wrist straps for that purpose but I have never had any issues myself. Just don't go dragging your stocking feet over a rug or rubbing a balloon in your hair before working on the PC and you should be OK. Open the side of the case and touch the metal frame before unplugging from the wall so the charge can go through the plugs ground. If you unplug first, the charge may have no where to go. Now get that balloon off your head and go to work!

Are you experiencing any issues? Any alerting beeps on startup?

If you're not. Then I wouldn't worry about it. A fan starting and stopping is normal (for the most part).