Processors have got a bit faster, and more memory is also good, but for basic computer work there's no need for anything fancy.
I can't remember how many years ago it was, it must be at least six but I bought a HP dx2000 desktop brand new and its still going strong.
If you want a cheap system then I've got some in the For Sale
If you want to take a look at yours free of charge and see if I can get it working with some spares I'm happy to do that too.
First thing I'd try though is replace the BIOS battery. There are some brands of motherboard which will not power up or display anything if the battery is dead or low.