ASUS P5B Deluxe and Intel Core 2 Duo 8500, BIOS inaccessible

My current config:

Motherboard ASUS P5B Deluxe (Bios 1236)
Intel Core 2 Duo E6420
4 x 1GB Ram PC5300
Win XP SP2

My computer was working properly. I just bought a Core 2 Duo 8500, I installed the CPU and no way to start, the PC gets stuck on the screen ASUS. I deleted the CMOS from the procedure on manual. But when I restart it, colors are blocking or the bios tells me 1 CPU 8500 3.16ghz. I can not access the BIOS setup button. Therefore impossible to set my bios.

I tried my Core 2 Duo E6420 and it works correctly. So, I do not understand what's the problem!

You certainly needs to flash your BIOS to a newer version that supports this new CPU 8500.

I am not an expert but according to me you must remove the battery and put the jumper to "clear".