If the HOLD button is red and MENU button is green, the phone may have corrupted firmware. In this situation, the phone may be attempting to contact its last known TFTP server to download a recovery image.
Please go to the following page on CCO and download the "7902_05_12_Recovery.zip". Follow the instructions provided in the "readme.txt" to attempt to recover the phone.
http://www.cisco.com/cgi-bin/tablebuild.pl/ip_phone_client
Please note that the recovery images included in the ZIP file are SCCP images. You will need to perform an upgrade again if you want to use SIP.