My computer worked fine for about a year but recently it seems there is a problem with powering the pc. SOMETIMES it will come on absolutely fine, but yesterday when I switched on the computer there was a small surge of power and then it died 
the longer I leave it off, the longer the surge of power till eventually it will fully come on and stay on. Also I can only turn it off by holding in the power button on the front until it shuts off. There is an on off switch at the back which does nothing when switched off, isn't that supposed to turn the computer off? I have been told that my PSU could be on its way out? If it has I was going to buy a new one myself..will it have to be the same as the old one or just compatible with the motherboard...how will I know whats the right one to buy?
the longer I leave it off, the longer the surge of power till eventually it will fully come on and stay on. Also I can only turn it off by holding in the power button on the front until it shuts off. There is an on off switch at the back which does nothing when switched off, isn't that supposed to turn the computer off? I have been told that my PSU could be on its way out? If it has I was going to buy a new one myself..will it have to be the same as the old one or just compatible with the motherboard...how will I know whats the right one to buy?