When you ran iprep and flashed the custom firmware, did you erase the flash drive, or is it still set up from the first flash?
If it is, then you might be in luck. Using iprep, you have the ability to flash the original firmware back onto the drive.
Shut down your pc, hook the benq drive up to the computer as normal, and load up iprep. When you get to the screen where it asks you to type in fben 1234567 12345, instead type in rben 1234567 12345 (type in the serial number of your console). If you backed up the flash right the first time you ran iprep to flash the drive, you should now have the ability to erase the drive and start again. Just follow the prompts from here, and hopefully you can bring it back to life.
A tip: When iprep asks you to turn the drive off and then press any key to continue, instead shut the drive off, power it back on, and then press any key to continue. If you don't do this, iprep will send the instructions to flash the drive prematurely, and it will not flash properly.
Good luck!