Restore iPhone 3GS - 4.2.1 = Error 1015 (Stuck in Recovery Mode)... Help!!!

Dear AfterDawners
I tried to restore my friends iPhone 3GS using 4.2.1 ipsw and now the iPhone is stuck in Recovery Mode. I tried to put the iPhone in DFU mode but cannot do that too. Every time I try the DFU procedure (Home + Sleep), iPhone's screen goes blank as it should do in DFU but reboots showing apple logo into Recovery mode(itunes logo and usb cable ) instead.
I tried downgrading but restoring with an older version ipsw doesn't even start.
I even tried a software called iREB to get it out of the Recovery loop (1015) but it just reboots the iPhone into recovery again.

I've put many iPhones in DFU mode before and got them restored successfully but this one I cant

Help!!!

 

FIX TO 3g ios 4.2.1 restore/ error 1015/ recovery mode loop/ Tinyumbrella cant fix
It took me all day to get my phone to work with the same problem. This is what worked for me. I will not explained to detailed, look for help elsewhere if needed.
1. look for and download ios 4.1 and restore with itunes (shift +)
2. restore will stop at error 1015
3. Use tinyunbrella to fix recover and then to exit recover mode
4. Use redsnow to jailbreak ( do not select update board you have it already)
5. Use cydia to unlock