can't upload sketches

I am having a problem uploading sketches to a Mega2560. This was working but stopped while using a Yun Shield which I have removed for testing. I am able to connect via USB to "Get Board Info" but sketch uploads fail with the following error messages:

avrdude: stk500v2_ReceiveMessage(): timeout avrdude: stk500v2_ReceiveMessage(): timeout avrdude: stk500v2_ReceiveMessage(): timeout avrdude: stk500v2_ReceiveMessage(): timeout avrdude: stk500v2_ReceiveMessage(): timeout avrdude: stk500v2_ReceiveMessage(): timeout avrdude: stk500v2_getsync(): timeout communicating with programmer An error occurred while uploading the sketch

To eliminate as many variables as possible I am just trying to upload the basic Blink sketch. The programming environment is a Windows 10 PC. 1.6.12 ide.

Any ideas?