XP rocks - best Microsoft OS ever and by far the fastest.
Everyone keeps saying "get rid of it because of security blah blah", but for power users who know what they're doing and know the OS inside out, security is no problem at all. I totally agree with your observations about updates too - no more updates = stability and no problems.
I use nothing but old systems (Server 2003 plus 2 XP systems) and haven't had any security issues in well over 15 years. I don't even have AV software installed because I know how to avoid those sorts of problems. It's just a matter of knowing what you're doing and security largely depends on how you use the computer and what you use it for. If I need Windows 7 or whatever for some reason, then I just fire up a virtual machine on the server. But my personal experience is that all the "newer" systems are bloatware and extremely slow when compared to XP.
Anyway, if reinstalling the program and drivers doesn't solve the problem, and you're sure that it's not a conflict with something else you've installed, then I would look at the hardware. I've had plenty of customers with similar software issues (as well as a few of my own over the years) that have turned out to be hardware related. It might surprise you that a lot of the time it's a faulty ethernet socket - usually an onboard one. For some reason, when NIC's fail, they can cause all kinds of strange problems which appear to be totally unrelated. Another common cause is a hard drive that "appears" to still be working fine, but is on the way out - you can usually hear the dreaded "knocking" in those cases.
Another tip, not so much related to software, but to boot issues, is a faulty USB device. Logitech wireless mouse/keyboard combos are famous for causing systems to boot straight to BIOS when the little USB receiver dies.
Let us know how you go with it.
Heaven doesn't want me, and Hell's afraid I'll take over!