If it doesn't light up for anything, even a voicemail or missed call notification, it sounds like you have a bug in the software that is keeping it from coming out of stand by. The method you described is a soft reset. It will reboot the phone, but not fully restore the phone's OS to it's factory state. If your problem is indeed a bug in the software keeping it from coming out of stand by, a hard reset would fix it. It will remove all installed programs, erase your contacts, SMS, email, etc. though, so make sure you have it all backed up before doing a hard reset. Here's the directions to do a hard reset from the HTC website:
What does a Hard Reset do and how is it performed?
A Hard Reset restores the device to its default settings — the way it was when you first purchased it and turned it on. Any programs you installed, data you entered, and settings you customized on the device will be lost. Only Windows Mobile software and other pre-installed programs will remain.
To perform a hard reset
Power the device OFF.
Press and hold the left and right Soft Keys
Keep the two buttons pressed, and at the same time, use the stylus to lightly press and hold the RESET button. If successful, you will get a black screen with white text asking you to confirm the reset.