Can not up load any sketchs to arduino mega 2560

First of I am running Windows 7, have a Mega2560. I have had it for about a week now and have loaded multiple sketches to it in the past few days and now it has all of a sudden stopped uploading new sketches. I was in the process of loading the Repetier firmware onto it for a 3D printer project and it just stopped excepting new sketches.

The error that i get is

avrdude: ser_open(): can't open device "\.\COM9: The system connot find the file specified.

avrdude: ser_drain(): read error: The handle is invalid.

Thank you for your help

Are you sure the Arduino is still showing up in your Tools->Port list as COM9?