i found method for this, its used with G3, so we need confirmation to be sure, if it may help you too.... it "shouldnt" be dangerous...but better wait for reply of masters here...i saved my machine with that one...
my english is so damn poor...forgive me,please...
-you need to format sd card to fat16(fat)
-kill wcescomm process from task manager on pc,
-find program named romupdate.exe, or mtty.exe
-go into bootloader mode, and plug wizard on usb,
-find in options of mtty(romupdate.exe) port, choose \\.\WCEUSBSH001
-now, press enter on main screen of mtty(romupdate),
-on >CMD type r2sd - it will make special header(and copy of os too, but its less important) which may help to make format with other method,
-wait 'till process ends,
-softreset pocket to get into bootloader mode...and do what machine says, its other method for format, when it ends, it "may" boot normally after softreset(you may try to do hard reset to confirm), even if it is not booting, format will let you to flash once more.
if it is stuck on bootscreen again, find info about rescue flash, now, it should be possible after that "format". If hard reset says "format failed" you wil not be able to flash anything - if it is not, you may do wantever you need, so try to flash wizard love, then any ROM with shelltool(yup yup its not typical for g3, but for me its ONLY method)..
i am not sure, if its useful..i saved one machine by that method...