Trouble ejecting portable drive

I'm running a PC with Windows7 and it's lately giving me grief when I attempt to eject 1 of my 2 external drives. It says something is using it and to try later. I get that message all day long and it's driving me nuts. I could eject the drive fine until a week or so ago. I've done nothing different and I've installed no programs. It works on the Mac at school just fine. The only thing I use this drive for is photos. PS and LR are closed. Not minimized but closed.

A Google search has had me bouncing all over the net for 2 hours chasing my tail.

Any ideas?

Drive Indexing or a Write Cache of some kind in play?

Antivirus scanning ext HD?
Get Process Explorer from Microsoft if you want to see what process is using the drive.

In the middle of moving so it's taken a while to get back to this thread. I have no idea what a drive index or write cache is. I didn't mess around with anything. I did download Process Explorer and it tells me TONS of stuff-none of which I can decipher.

Now the drive won't eject on my laptop, either. Grr. I've got Kaspersky on both computers and have had it for about a year and a half. I've changed nothing manually as I don't know how. The laptop ejected the drive the last time I used it on Friday. Both systems are Windows 7.

Now is a good time to take a break and have some lunch. When jumping up and down on my computer while foaming at the mouth and screaming obscenities seems like a reasonable thing to do, you know it's time for a break.

Edit to add info...

PE says 13 things are going on with my external drive. iexpore.exe, several outlook.exe and several sidebar.exe. Not sure why they are using the external drive as I have nothing but photos and LR stuff on there.

PS Lunch was tasty!