Hi. I'm having the same issues on 2 different machines.
I'm familiar with Linux but still a Newbie.
This is a several part post and I will do my best to break it down in to easy to follow steps.

Hardware:
Computer1...Amd64 CPU 3.0Ghz
1Gig DDR RAM
ATI onboard Graphics

Computer2...Amd Sepron CPU 2.0Ghz
1Gig DDR RAM
Nvida onboard Graphics

Both are able to boot via USB, DVD/CD drive, PXE, Hard Drive, SATA
Both are 64-bit (I have tried both 32-bit & 64-bit with same results)

Disto's tried on both:

Fedora 16
Debian Sqeeze
Gentoo
Ubuntu

Microsoft Windows XP Professional

Problems:
Ok, the first problem as it needs to be addressed first in order to address the rest is the loss of video only under Linux but works fine under Windows.

I only installed Windows on a separate hard drive to test and trouble shoot.

I can boot the install, and go through the install process just fine under all the above distro's except for Gentoo (I'll get to the Gentoo issues later).
After Install completes successful, disk is removed followed by a reboot. I have video all the way through the Grub boot selection Menu. This is now where I start to have my issue...it's starts the load process and will sometimes get half way down the screen but most the time it won't before I loose all video. I have let it sit for, as long as, up to 5 hrs to see if it comes back but seems to just be hanging the entire time, resulting in a hard shut down.

I have replaced RAM, Power Supply, Drives, and have even tried other video cards but nothing has worked.
I also tried a different monitor and still got the same.

After several times and still no change, I then installed Windows XP Pro just to see...It worked just fine with video the entire time.

I have also tried using the -- vga=800 with the boot and only worked for the grub and no further.

On a side note...I did have Debian and Fedora duel booted on Computer1 with no problems but after I shutdown for bed and then got up and went to boot up the problem was there.

*moderator if there is a better place for this, please move to the right spot. Thank you.*

Both Nvidia and ATI video may require you to install the correct driver. The exact steps vary from distro to distro. For example, in Ubuntu you'd use the restricted devices manager jockey-gtk. It is required that you identify your specific video chipset and choose the correct solution from your distro's documentation.

Personally, I do not install until I have found a distro that works well as a Live CD for several days. It is a frustrating waste of time to go through the entire install process only to discover one's hardware is unsupported!

I just re-downloaded the Ubuntu live cd so I can reburn it to disk. I'll give that a try and see if it works.

I intend on actually installing a distro that can be built from scratch as it would give me more scalability for what I need.
In the mean time I need to get a stable and usable distro installed to build the install on as the Windows machine that belongs to my roommate is just to unstable to handle the job.

Ubuntu can be built from scratch too: http://www.psychocats.net/ubuntu/minimal

Although to be frank I do not understand why someone would install Ubuntu as an intermediate step towards not using Ubuntu.

Hi, this may help.

when installing the distros, use the vesa video driver until you get all the spec's of your devices.

Once you have booted into X, (where your sys seems to stop) you should get a full gui (kde, gnome, etcetera).

Now you can search for the correct/better driver.

at your point now (above), your keys probable don't work either when you get the black screen, try "ctrl-alt-F1" (/F2 thru to F8 or even F12 on my system).

If you get a command prompt, login and as root type "init 3", this would take you to cli land, and shutdown the failed X-server.

If you can get this far, then edit the /etc/X11/xorg.conf find the graphics driver line and edit it, to say vesa.
(you might do this edit with a live-cd)

save the file and type, "startx"

Regards Glenn

edit, the vga=800 statement will only control how the kernel displays text on the screen and the grub-boot gui resolution. I use vga=794. There is a list of these,

Thank you everyone that has replied to this. I have tried everything suggested and at least have this part working now.
It turns out that I feel like a complete idiot as the problem was actually a bent pin on the vga connector . I had some how over looked it and didn't even see it until replacing a video card. Once I straightened the pin everything started working again.

As for the other problems I can now post those under the correct sections individually.

Again, Thank you for your help.