Service pack 3 crash after fresh install on nvidia chipset?

Anyone know why when installing SP3 on to a (Brand New) system with nvidia nForce 630i chipset, service pack fails then trys to roll back then no startup in windows except a black screen and mouse cursor. Tried safe mode same as normal >just get black screen. tried all boot options last known, safe, vga etc. can't get into windows This was a clean install and everything was running all evening, all programs loaded, ran and installed no problems. This is not virus related so don't bother telling me. Went through all the 119 windows updates no problem after restart until I reluctantly done Explorer 8 and SP3 then bang! 4 hours of work wasted. Some help would be appreciated.

System is a Gigabyte GA-73PVM-S2H motherboard (Latest F8 BIOS) with an Intel E5300 core 2, on board nvidia7100 video, 2 Gb Kingston DDR2 (tested with memtest86) sata WD 640Gb HDD . Arctic Power 500watt PSU.

Windows XP Pro 32 Bit. BIOS at defaults no overclocking. system temps are very cool.