1.open redsnow latest version

2.browse file 4.2.1 3gs orginal firmware

3.select only this option ( just enter pwned DFU mode right now)

4.then flash with this MEGAUPLOAD - The leading online storage and file delivery service custom firmware

5.after finish flash Do redsnow jailbreak procedure

( if new bootrom means stuck in apple logo after jailbreak pls dont try to flash again just do with redsnow JUST BOOT TETHERED RIGHT NOW option and wait for boot)