This is my 2012 Optiplex 390.
It's in excellent shape, and it's got a 3.1 GHz Intel i5 processor and 8GB of DDR3 desktop RAM. I can provide a spec sheet if necessary. It has frozen up multiple times in the past, but it might've been due to the OS I was using. Maybe use Windows 11 or Ubuntu.
I've tested all the components, and, if it's a hardware issue, it narrows down to either the CPU or motherboard. You can score a new CPU for anywhere from $35 to $100 (It depends on which CPU you find. I suggest the Intel i3-3225), and you can easily get a new motherboard for $25 (like this one: https://www.ebay.com/itm/255236227671? ).
Asking $60, cash only. Comes with power cord.