If it's old is most probably the power supply.
You can order a new one and easily install it. (is a no brainer)
My old one (2007) died a while ago, I replaced the PSU and is working like a charm ever since. The new revised PSU is also better, noise free when you turn it on and I believe is more robust.
If I recall correctly the PSU costed me around 60 Euro.
Edit: Yep! I've checked and it was 52 Euro plus shipping.
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