PC keeps freezing up

I’m having an issue with an aging PC—about 8 years old now. When I power it on, it randomly freezes up; it could happen during the boot process, while I'm gaming, or even just idling while browsing the web. Once it hangs, the whole system becomes completely unresponsive.
I’ve already had technicians swap out the hard drive, and they assured me it would solve the problem, but the freezing persists.
Any help would be greatly appreciated.

What kind of technician tells you "it'll be fine" without actually checking anything? Is that guy even human? 😁 Does the computer just reboot after freezing up, or are you getting a Blue Screen of Death? Also, could you list your full specs? You might want to pop the case open and check if any of the capacitors on the motherboard look bloated—that’s a classic sign of trouble. It's also worth grabbing Crystal disk info to see how your hard drive is holding up... and maybe run a scan with Malwarebytes just in case there's some junk software lurking around. There are plenty of ways to dig into this.

It won't throw an error code; it just freezes up entirely.
There aren't any blown capacitors.
I'll send the configuration once I get back home.