20 Most Recent Gigabyte RADEON X800 Pro VIVO GV-R80P256V (256 MB) Graphic Card - Page 3 Questions & Answers

obviously you have a cable connected wrong somewhere. You have a power & ground lead reversed somewhere in a connection...could be anywhere. If you don't know what you're doing, hire a professional.

2nd one down on this site should be the one http://www.driverscape.com/download/nvidia-geforce4-mx-440-with-agp8x-%28microsoft-corporation%29

1024 megabytes in one gigabyte

PSU could also be playing up and not giving correct voltage to motherboard - check outgoing voltage from PSU with voltmeter and check product standards for that model... If ok then it could be the motherboard itself - all it takes is a capacitor or transistor/logic gate(switch) and it will start behaving unusual...

check BIOS: it should read IDE (not AHCI) mode!

yes it supports

PC PartPicker says it will https://au.pcpartpicker.com/list/

yes your motheboard supports socket 775 cpu, here is the maufacture website that will list the cpu support list http://www.gigabyte.com/support-downloads/cpu-support-popup.aspx?pid=2557

Try here Windows 7 Ultimate

DOWNLOAD THE DRIVERS FROM GIGABYTE.

Try reflashing the BIOS again.