HP Photosmart C4280 All-In-One -- mystery program prevents its use.

Hello,

I have an HP Photosmart C4280 printer/scanner, running on an HP tower
with Windows XP. I installed it about a month ago, and it worked.
Then I unplugged it and ignored it for a month. Yesterday I plugged
it in again, and POOF! it doesn't work. Instead, I get this error
window message:

"The function you have requested cannot be performed because another
program already has control of the device. If the program currently
using the device, save any unsaved work, close the program, and try
again."

Yes, yes, that's ungrammatical; but that's what it says.

I turned the computer off and on. Same thing. I hadn't opened any
programs, except HP Solutions (the HP-recommended way of starting the
device).

Hit Ctrl-Alt-Del to see what's running -- and the list of active
programs is empty.

Process Manager says there are severel processes running -- but there
always are -- and all of them are taking 0% of the CPU.

Something or other -- I forget what -- says that the driver IS
correctly installed.

Any ideas?

Thank you!

Ted Shoemaker