I have a hp pavilion a1637c: AMD Athlon 64x2, 500G HDD, 4G RAM.
I have several times installing Ubuntu. I get to the point where it boots up to the desktop but it never loads up. The Ubuntu screen that comes up just fills 1/4 of the screen, it has no option to log on.
I have also installed Xubuntu & Kubuntu, they give me the desktop screen 1/4 size and it has the little loading dots that are active, then the full screen goes kind of dark purple.
In all the cases I wait for aprx. 45 mins to see if it begins to work.
I did a successful install on my Windows 7 screen.
NOTE: I used the WUBI for all installs