I also have a couple Dashes. One will turn on, screen lights up, windows boot sounds play, but the screen is solid white. Any ideas? I haven't tried reflashing but I didn't see how it would help. Although, I don't know if it's a physical problem since the screen does light up...it just stays white.
The second dash was running unbelievably sluggish and I could not navigate the start menu to format it. I decided to update the firmware to the newest one on T-Mobile's site, which went well, but then when I restarted the phone...it would freeze momentarily at the splash screen/animation, then go to "auto configuring" and when it hit 2% would always turn off. When I restarted the phone, it would give me a BSOD (sweet! didn't know they exist in WM) saying the device was unexpectedly turned off, possibly due to the battery being removed or low power. When I pressed ok (or yes, can't remember), it'd go back to the auto configure and turn off again. I tried a few times, no luck, and tried reflashing but couldn't since it wouldn't load the OS. Oddly, while typing this thread, it fixed itself.