Impossible to say. I've got a a PC still going strong after 10 years (as you may guess it does have its limitations!!!) and I bought another that gave up the ghost after 2 weeks (since fixing it has not missed a beat). If components are going to fail then they tend to fail in the first few weeks. Provided it's not been mistreated a second hand one from work should be no trouble - just remember that the specs will be 4 years old or more so may have difficulty with some of the latest software but I don't think that will be problem from the sound of it.

I'm writing this on an 8 year old laptop my wife got from her job when she left for the princley sum of £1. It got a bit slow in Windows so it's now runing Ubuntu Linux and Open Office (it's free and legal ) and is used for web browsing, bits of word processing etc. and it boots up faster than any of the newer PC's!

If it's at a good (or even silly price as some work PC's are) I'd go for it.

Take the case off and get the Dyson in there - often, they make noises like that due to a build-up of dust on and around the fans.

Also, consider flattening the HDD and starting again - that can help.

Alternatively, get the Mac and become one of the cool kids!