My phone also didn't turn on any more after flashing. This is what I did:
I removed the battery and plugged in the power adapter. After a few seconds or minutes the display switched on and showed that there is no battery. After putting the battery in again I could turn the phone on again.
Then I followed a tutorial I found here (the first comment): the Unlockr
For those who faced the "death step" or "black screen" and can't get the phone recognized over USB on PC/MAC, here is a solution (step by step):
1. Put your MicroSD on your computer with an SDHC Adapter.
2. Now open the MicroSD and paste "LCR_1.7.3-signed.zip" (use THIS and not the 1.8.2) renaming as "update.zip" on the memory card.
3. Press "Volume minus + Camera + Power" and wait to vibrate 3x then leave it booting.
4. Now the system will get automatically your update.zip file and rebuild the system.
5. If the update don't happens please enable UMS and ROOT on the menu and then "Reboot the system".
6. Now you can switch OFF removing the battery and ON with power button.
7. Wait to boot into the LCR MOD custom system, it will be really slow... be patient.
8. If it crashed try again with the fastest move you can before it crashes on some important steps =D.
9. At the HOME screen go to "System -> Applications -> Development -> Debugging mode".
10. Now your PC will recognize the phone and you can use the "A1 DL tool intra" to load any Eclair or Froyo BIN image if you disliked the speed from LCR ROM.
My Liquid has now the "Acer_LiquidF_0.007.00_EMEA-GEN1_05.01.01_57ab23c1cf32cd66f8b94e4be24993d4.bin" from FROYO on it. If you still want custom ROMs then try to use the superboot with a newer zip update, but i won't recommend you to do it again... it's not worth anymore.
Hope it will help you.