The question not quite asked is:
"Can roaching a PC onto an old machine make it better than it was, hopefully as good as a new machine but for less money?"
The general answer is "no". ... but a lot of money has been burned, trying.
As has been pointed out, generic cheap PCs are not well suited to industrial environments. Bulletproofing them costs a lot of money. Bulletproofing them slowly, as you learn, costs more.
If the fundamental machine is sound, you can perhaps add capability by replacing old simple industrial control modules with new ones having extra capability. For temperature control in particular, newer modules can be had with network connections that allow monitoring and/or control by PCs located in a benign environment. But do not underestimate the cost of software to do that. Start small and limited, and don't try to do anything with custom software.
If the fundamental machine is worn out, call a scrap dealer to haul it away, and buy a new one.
One sort-of exception is very old, very big, very heavy machine tools. Nobody builds 'em heavy anymore, so rebuilding and retrofitting CNC and such can give you a machine that you couldn't buy new for any amount of money. You still need to bring your wallet.
*** If you haven't done something like this before, don't start with a unit that will put the company out of business for as long as it's down. Start with some offline process that isn't a bottleneck.
Mike Halloran
Pembroke Pines, FL, USA