There have been a lot of questions like this, however mine differs, so don't lock this one as a duplicate just yet.
Others have the problem that they only see categories with missing icons. I'm not seeing anything. It doesn't say "No items match your search" either. It worked before, even this morning. I can't say what I did that broke it, though.
Windows 7 troubleshooting couldn't find the problem, I restarted the Windows Search service, and I rebuilt the search index, but none of that fixed my problem. The problem has appeared before on a different PC also running Windows 7, but I can't recall what caused it, nor what fixed it.
I can verify search working in Windows Explorer, so it isn't search itself that's broken.
Any help is appreciated, as I use this feature quite often.
(Late) edit: the issue seems to have fixed itself after a reboot.