Sorry. I haven't seen that GPU in years. Not well supported internally by Xorg... likewise, causing your specific problem. But the good news- The ASpeed site does have linux drivers to download for your hardware. Current from them is file v96_whql.zip. In that archive, go the the linux folder and extract "lxdrv.tar.gz". After extracting that, read the readme file. Before executing the install script, you have to create your own blank xorg.conf file with the SECTION DEVICE, driver line pointing to "ast" driver... and you have to set the properties of the install script file to be executable. Their install script includes checks for "ubuntu".
I think I remember that it may still only do 2D graphics and not 3D... but they may have got around that, not positive on that. It's been awhile. That is how it used to be with that GPU in Linux.
After you install the new driver (including rebooting to use the new xorg.conf), then run:
That will output the capabilities of your GPU using that driver... And if it is capable of running Unity 3D or if you will have to run Unity 2D. If still just 2D graphics capable, then Unity 2D is not installed as a fallback any longer, so you'd have to install it to be able to use Unity 2D for the DE.
Hope that info helps.