Ubuntu Is Broke!

I’m trying to start Ubuntu on my PC at home, but here’s what happens:
Loads the start screen

Set the VGA to 800x600x16

I enter some boot parameters (noapic, nolapic, debian-installer/probe/usb=false, gdth=disable:y)

Select “Start or Install Ubuntu”

The “Loading Linux Kernel” box comes up, completes.

The Load bar comes up, loads a little bit, then the computer restarts.

Also, when I used the onboard graphics instead of my ATI Radeon 9200, it loaded, showed the little “X” cursor, then went to a black screen and hung. Without the boot parameters, it loads partially, then goes to a black screen with error messages scrolling down in very very fast, then reboots.

My machine is custom built:
ATI Radeon 9200
Sony CD Drive
70GB Harddrive
PS/2 Keyboard and Mouse
Intel Celeron 2.93 GHz processor

Ideas, anyone?