Good. OK, now we need to know the exact model of the motherboard.
Possibilities include:
p5b-mx
p5b-Plus
P5B-VM SE
P5B Premium Vista Edition
P5B-Plus Vista Edition
P5B-MX/WiFi-AP
P5B/TeleSky
P5B-VM DO
P5B-E Plus
P5B-E
P5B-V
P5B-VM
P5B Deluxe
P5B Deluxe/WiFi-AP
P5B
Several of which will take different BIOSes than others.
If you are talking about the plain vanilla P5B, then you will need BIOS version 0201.
ASUS has a (not very helpful) guide to finding your BIOS revision
here. It won't help in your case, but it will help you find your motherboard revision, which you can use to maybe find which BIOS it shipped with.
Usually, the power light will blink every second or so if there is a power problem, or a processor incompatibility issue. This leads me to believe you have faulty equipment in there somewhere. you've tried 2 different video cards, right? Is your motherboard SLI-capable, and if so, do you have it set in the correct mode (non-SLI)? The P965 chipset (which is used on all P5B boards) is very picky about RAM. It has something to do with voltages, possibly someone else can field this one. I just know you basically have to have approved RAM to get the thing going the first time, then you can tweak your settings in BIOS and pop in your overclocking RAM, if you want.
So, go through the motherboard setup section of the manual one more time to make sure you didn't miss anything. Check your SLI switch (if you have one). Check to make sure your RAM is compatible with P965. Get us the exact model (and possibly even revision, following instructions I linked to above) for your motherboard. We'll get this narrowed down.