Can you give us any details on the dead PSU? Make, model, age...? If it's a no-name cheap thing that was already old before you left it for five years, my guess would be the capacitors.
Edit: the simple explanation is the capacitors, which are normally an open circuit to DC, have degraded as a result of not being used and become a short circuit (or at least low impedance), overheated then exploded. They're known to explode when they go wrong, they're even built with a weak point so they don't explode like tiny frag grenades and cause injuries with shrapnel flying everywhere, there's usually a lot of smoke involved too.
The psu was old don’t know when I got it , it was bagged as hiper 520 w , it had older type molex connectors not sata type. I can’t tell you anymore as it’s gone in a scrap rubbish skip at work.
That’s what I thought cos when I took it apart yesterday to see inside it it looked like they had shorted out and melted from the heat , they were the only damaged pieces in it.
I have ordered an evga 600w psu should arrive tomorrow thanks again.
Just did a quick search that make are on sale on eBay going to stay away from that brand I think.