Computer completely frozen

[madharuhi]

Do note that problem was already solved, but I still have queries about it.

I had a BSOD while several torrents were running, and when I came back, it did the usual hash check. Midway through, everything on the computer starts to slow down until it comes to a complete halt (the cursor can be moved for a while before it freezes up too). Alt+Tab, Alt+F4, Ctrl+Shift+Esc (or Ctrl+Alt+Del) does nothing to help (Task Manager does not appear). Only option left was to do a hard reset on the computer.

I checked every torrent manually starting from the one at the bottom of the queue, and eventually came down to one particular torrent (I'm pretty sure there's no virus or anything wrong with the contents of the torrent). It kept getting stuck at the same percentage when doing a hash check and after a minute or so, the freeze occurs.

I've since deleted the torrent and the incomplete download, and re-downloaded it and it works fine now. But question is, what actually happened? It should have hash-checked fine.