Cannot type shift s for capital s

I wouldn't be here typing this if I hadn't tried everything else I came across on the internet.

My story goes like this: at some point today, my keyboard became incapable of giving me a capital s when typed with either shift key, but it's perfectly capable of typing the letter s in lowercase. I can do the caps-lock s if I want it capitalized, but I'm already conditioned to doing single capital letters with the shift key, so I really don't want to convert my entire way of typing. It doesn't even seem to matter what application I use, if I have the ability to type, I can't type shift+s for the capital s.

Based on various articles found online, I've been through checking keyboard shortcuts, even restoring them to the detaults (because by default, there shouldn't be a shift+s shortcut for anything, obviously), and even checking, double-checking, and changing the text-to-speech shortcut (which is also turned off, as I don't need it in use).

The first thing I tried doing was to restart the computer. As laughable as that is, I've been around computers long enough to know it's actually a valid way to resolve minor issues. No luck. I even repaired permissions, and verified and repaired the hard disk (of which, there was nothing to repair at all) by using the disk utility on the snow leopard (10.6) disc.

The most recent addition to my computer has been a wireless mouse, a Logitech m510, which I bought about a week or two ago, but things were still working fine on the computer after adding it. I added the Logitech Control Center software for grins and giggles that same day, which really didn't change anything. As for the keyboard, a Logitech G110, I've had this for at least a year and have been using it without issue.

Any suggestions would be greatly appreciated. I'm sure I'm not the only person who has had the shift+s issue and not have it related to text-to-speech.

Thanks in advance!