Use the Bootloader to reset
If you aren't trying this from the bootloader you should try that, you will need to disable Fast Boot under the Power menu in your settings. Turn the tablet all the way off, and then power it back up by holding Vol - and Power at the same time until you get the BugDroid's skating across the bottom screen, you use Vol +/- to navigate and Power to select, one option should be a factory reset.
IF you are already trying it this way, I dunno what else you would do other than placing a factory ROM zip and having the bootloader flash it!
My HTC Devices:
HTC Passion (Google Nexus One) - Nice screen!
Current ROM: eViL's NXSense v1.26 (My dad uses it now)
B]Galaxy Tab 10.1[/B]
HTC Pyramid (HTC Sensation 4G) - Blazing fast, understatement
Last ROM: Virtuous Quattro (Latest)
HTC Flyer - HTC on the Big Screen!
Last ROM: FlyHoney ROM v0.2
HTC Ace (HTC Inspire 4G) - Left AT&T!
HTC Rhodium (AT&T Tilt 2)
HTC Raphael (AT&T FUZE)
HTC Kaiser (AT&T Tilt)