Lost my hand tool! What have I done?

I've been working away in Photoshop all day, and all of a sudden I can't use the spacebar as a quick temporary shortcut to the hand tool for scrolling around while zoomed in on my images..

I'm sure I've inadvertently set a switch via the keyboard somehow, but what have I done? More importantly, how do I undo it?

I'm so used to using that shortcut, that I practically can't operate the program anymore!!

Any help is greatly appreciated!

EDIT: Never mind -- a second restart seems to have cleared it up. %#^%#*@ computers!