Never mind. For some reason my remote wasn't entering cable mode (weird, since it's never been a problem before today). In case anyone else has the same issue, the solve is:
If your remote control doesn’t respond when you press a button, the remote may not be in Cable Mode.
To put the remote in Cable Mode: • Press the Cable button. • Take the batteries out of the remote and put them back in. • Press the up triangle button on the front of the converter box. • Replace the batteries in the remote. • If your remote doesn’t work after trying all of the above, you may need a replacement. Call 1-800-COMCAST (266-2278) to request a new remote.