I did some thinking and thought that getting it to boot by trying and failing to use an RUU, downgrading it, rooting it there, and then flashing another rom would solve my problems.

I managed to get to downgrading and rooting the phone, but after apparently flashing cwm through rom manager, I turned off the phone and tried to boot into recovery by vol down + power. Those are the buttons I use to boot my g2x into recovery, and through searching I didn't find any other combos for the g2.

That didn't work. I got sent to fastboot again, and no buttons work. I then tried RUU again, and this time it worked, booted. I turned it off and back on to see if it would actually load the rom this time. Alas, fastboot screen again. Still no working buttons.

I tried the PC10IMG.zip again. It flashed, but when it says <Press power to reboot> and I press power, I get sent to fastboot.

I pretty much consider this phone a lost cause, but if anyone has a suggestion that might help, please tell!

I can only tell you that I have same problem, just happened to me y/d and I am stuck on white HTC logo not having adb access and can not flash any stock rom for signature errors. not sure how to continue. thread is: http://forum.xda-developers.com/show....php?t=1614042, good luck for both to solve it