There is no currently supported version of Ubuntu which supports SiS 671/771 cards (this is bug #301958). Your options are:

• Use an obsolete unsupported version of Ubuntu and never update. Not really recommended since you will not get security updates, but if you want to try it then 12.04.2 has been reported to work.




• Try Linux Mint 13. There have been reports that it contains some older modified SiS driver that works.




• Give up and buy a laptop with supported graphics. An old Thinkpad with ATI graphics can be bought for $50 on Ebay and it will run Xubuntu/Lubuntu well.




• If you are a developer, you can fix the source. The issue has been brought up on the Xorg mailing list, and an Xorg developer responded (1 2)

  
  
  

  
  

  If those still don't work, get your hands dirty... if any particular
  strings appear in error messages, find those strings in the source and
  figure out what function is failing. Then compare the execution of the
  broken copy to the last working copy you remembered. If the API of
  some dependency changed, use git bisect to repeatedly compile the
  kernel or the Xserver until you find the exact line of code in the
  dependency that made the difference. Hacking the driver might sound
  hard, but it's not so hard that you have to pay someone to do it.

  
  
  

  The problem here is not that some gigantic reverse engineering effort
  is needed. The problem is that a few tiny janatorial fixes were
  required. And it's easy to miss one when the developer implementing
  the fixes doesn't have a SiS card on which to test.

  
  

Basically nobody knows what the actual problem is, so someone with the affected hardware needs to git-bisect the Xorg driver source and figure out how it got broken.

Related:

• How to enable 3D acceleration with Sis Vga 771/671 on Ubuntu 12.04


• Ubuntu 14.04 screen resolution too low (SiS 671 graphics card)


• How to install SiS 671/771 Video Drivers in ubuntu?


• How to install SiS 771/671 video drivers on 13.10?