[SiS] 771/671 chip graphics card problem

[James e]

Hello All,
I have been using an old version of Ubuntu on a Clevo W76S laptop and in a monent of madness (it now seems) i updated it to the xubuntu operating system when it asked me if i wanted to.
Well, the screen resolution went to pot and i got very cross with it i put it in a draw for a year.
So, two days ago i had another crack at fixing it i wiped it clean and put on Mint Cinnamon 17.1 Rebbeca 64bit. (it is a 64bit computer i think).
I now have the same problem.
Looking around the net and this forum it seems that the graphics card/ chip is the problem - the driver manager says that no proprietary drivers are in use and the Display settings can't be changed from 640 x 480.

I have read the other threads and tried typing sugested lines in the terminal but, whilst i'm learning, i really am one of those monkies at the typwriter managing to produce "to be or not to be" by shear blind luck. Thus i've not discoved anything other than a profound sense of how little i know about computers.

As i saw on another thread i typed inxi -b in the terminal and this is that i got back...
james@Hal9000 ~ $ inxi -b
System: Host: Hal9000 Kernel: 3.13.0-37-generic x86_64 (64 bit) Desktop: Gnome Distro: Linux Mint 17.1 Rebecca
Machine: System: clevo (portable) product: W7x0S version: Rev. A1
Mobo: clevo model: W7x0S version: Bottom Bios: Phoenix version: 6.00 date: 12/21/2009
CPU: Dual core Celeron CPU T3000 (-MCP-) clocked at 1799.511 MHz
Graphics: Card: Silicon Integrated Systems [SiS] 771/671 PCIE VGA Display Adapter
X.Org: 1.15.1 drivers: fbdev (unloaded: sis,vesa) Resolution: 640x480@73.0hz
GLX Renderer: Gallium 0.4 on llvmpipe (LLVM 3.4, 128 bits) GLX Version: 2.1 Mesa 10.1.3
Network: Card-1: Silicon Integrated Systems [SiS] 191 Gigabit Ethernet Adapter driver: sis190
Card-2: Realtek RTL8187B Wireless 802.11g 54Mbps Network Adapter driver: rtl8187
Drives: HDD Total Size: 320.1GB (1.5% used)
Info: Processes: 148 Uptime: 18 min Memory: 457.0/3685.0MB Client: Shell inxi: 1.8.4

I think that i need to download a suitable driver from some where but i don't know where or how.
If i can't fix it because it is such a poor graphics chip, could i get the computer to work with a MATE version or would i get the same problem?

Many thanks in anticipation,
James