There's often a fuse in the PSU, although it's usually a pain to get to, and potentially dangerous if your not electronically savvy.

I'd question the merit of doing this anyway - unless the fuse blows when you are there because of some stupid mistake, it's probably not the fuse. From your post I infer that you leave your PC on a lot (or 24x7). Eventually the PSU fan is going to fail which will cause heat build up, and can lead to the or other part of the PC (especially if the PSU fan was the only case cooling) failing.
But I'd guess the PSU has failed.