Was it a single Windows Update or several? What was it an update for? If it was only one update, I'd probably try uninstalling that single update to see if that made things work again. As much as I don't like this option,  a System Restore to sometime last week might be worth trying too.

None of the above would explain why it won't work on multiple PCs but I'm using 2 Chilis on a Windows 7 x64 PC without any issues. One thing I'll say though is that I actually disabled auto-updates because I didn't want it restarting in the middle of the night and losing hashing time. I just check for and install them manually once a week or so but its a very bare bones PC with little more than mining software on it.