Nano v3 won't upload now

I have a Nano v3.0 and a Uno R3. Both were working great with Arduino IDE 1.5.3. However, yesterday suddenly the Nano stopped uploading properly. I have selected Duemilanove as the target, which was working. Now, for no apparent reason, when I try to upload a sketch, I get this message:
"avrdude: stk500_getsync(): not in sync: resp 0/00"
Can anyone give me an idea of why this suddenly started happening? The UNO still takes the upload successfully. I should note that when I plug the UNO into my computer, it registers as Arduino on Com4. WHen I plug the Nano into the same USB port, it registers only as USB on Com5.
Thank you for your help with this...

There may be an issue with FTDI & nano clones.

Search for 'arduino nano ftdi TEST'

Can you use the UnoR3 to reboot the Nano with an Uno bootloader?