Windows 7 - Weird problem with the pc

Dear colleagues,

I have this weird problem. When I switch on my pc, it starts buzzing but isn't displaying anything on the monitor. And it continues like this for like half and hour and someone must perpetually reset it until it starts working OK. Could you please tell me what's the problem?

Thank you !

Best Regards
Stefany

You think have a bad Power Supply Unit, you may want to replace it as soon as possible, a bad power unit is nothing to take lightly. I think you should try to use it as little as possible, or not at all if you have another working computer around the house.

Thank you so much for the answer, but since I am quite ignorant, could you please explain what Power Supply Unit means?
We do have another computer in the other room that is connected with a router to this one, but we usually switch on this one before the other one.
Thank you!

The Power Supply Unit, usually called "PSU" amongst the geek community is what supply's the whole computer with the power it needs to operate. Most power units today being around 300 Watts or more.
The reason I believe the issue is the power supply is because of the buzzing sound you are getting which could be a capacitor giving up within the unit.

^^ Thank you, thank you, much appriciated!