will not pass "deadmanCheck" soft reset chip

this is my rig:
Processor: Intel Pentium D 805 2.66GHz ovk@3GHz
Motherboard: Asus P5LD2 REV 1.0
Memory: 4G DDR2 667MHz Corsair XMS2(ram is @800MHz but a can't run at 800MHz cause of my CPU)
Graphic card: Sapphire HD4870 1G DDR5
Display: Samsung SyncMaster 223BW 22"
DVD-Rom: Asus DRW-1814BLT SATA
Hard drives: 1. 500Gb Hitachi SATA II, 2. 1T Hitachi SATA II
Keyboard and Mouse: USB
OS: Retail Mac OS X Leopard 10.5.8 (voodoo kernel 9.8).

These are my problems.
Now I have a new graphic card (HD 4870) and before I had an Ati x1600.
Both works fine (qe/ci enabled, rez change) on Leopard.
When I had the x1600 I've managed to install Snow Leopard about 3-4 times (each time i mess it up by tring to make sound and the graphic card work...kernel panics).
After I got the HD 4870 I made a clean install of Leopard (repartitioned the 500G , one partition of 100G for windows 7 and the rest for Leopard).
Leopard works just fine, fully updated, sound works using AppleHDAPatcher...internal speakers work, front headphones work, microphone works, haven't tried Line in and Digital output yet, and the graphic card works flawless using ATY.pkg from iAtkos v7.
I have 2 network cards...on board ...marvel yukon, on pci realtek, both works by default on Leopard, and also worked on Snow Leopard.

I've tried to reinstall Snow Leopard to see if i can get the HD 4870 and sound working, but when I boot the install dvd (using -v) it won't get passed checking marvel yukon...it says ...deadmanCheck...soft chip reset...then gives some errors...then again with deadmanCheck. I've tried to install Snow from inside Leopard…but again the same issue. Need to mention that I've bought a copy of Snow Leopard and restored it on a partition on my 1T hdd. Also I'me conected to internet trough a wireless netgear router wgr614 v9.

Can someone help me?