Yes, it's that PC you built for me. Up until now, it's been working perfectly.
And it has nothing to do with the Start screen or any of the "tiles". Basically any time the cursor moves over a control bar- any part of the standard Windows Taskbar, mainly, but it's done it with Paintshop as well- the computer locks up.
As in the keyboard doesn't do anything, the cursor disappears, and if I have an MP3 playing, it starts repeating the same one-second or so bit when it locked, until it frees itself up again.
For the time being, I can keep working; everything's fine as long as I keep the cursor away from the taskbar. Although as 8.1 was wont to do, every now and then as you're going from one screen to another, it tries to open the pop-up control panel, which locks it up again.
As I said, it "rights itself" after a minute or two, and I can go back to working, but it's still a major annoyance.