Nick wrote:

higher? Im on 300 Watt

So what? If your +12v, for example, is only rated at 10 amps, and you need
11 amps at start up, you might need more power on the +12v. Total power
doesn't mean squat if an individual output is under powered.

Nick wrote:

Sometimes when I switch my PC on it switches off after about 1 second.
When
I do it again it works as normal. Is this a sign the power supply is
about
to burn out?

Not necessarily. Could be it is underpowered and one output trips its OC
protection circuit sometimes. That would be my guess with no further info.

Try disconnecting the PSU from unused components and see if the problem
goes away. If so, you need a higher powered PSU.

--
Better than hearing "Lady Day", or checking in at Monterey...