Screen locked at 640X480

My aging machine has only just been installed with 9.10.
At first it started with 1024x768 resolution, then dropped to 800x600 randomly.

Then I tried to fix it by following a suggestion to install Nvidia drivers (not recommended) - silly me.

Now the machine is only permitting 640x480 resolution or less.

Any ideas - none of the answers i have looked at seem to work.

lspci reports :

00:00.0 Host bridge: Intel Corporation 82815 815 Chipset Host Bridge and Memory Controller Hub (rev 04)
00:01.0 PCI bridge: Intel Corporation 82815 815 Chipset AGP Bridge (rev 04)
00:1e.0 PCI bridge: Intel Corporation 82801 PCI Bridge (rev 11)
00:1f.0 ISA bridge: Intel Corporation 82801BA ISA Bridge (LPC) (rev 11)
00:1f.1 IDE interface: Intel Corporation 82801BA IDE U100 Controller (rev 11)
00:1f.2 USB Controller: Intel Corporation 82801BA/BAM USB Controller #1 (rev 11)
00:1f.3 SMBus: Intel Corporation 82801BA/BAM SMBus Controller (rev 11)
00:1f.4 USB Controller: Intel Corporation 82801BA/BAM USB Controller #1 (rev 11)
01:00.0 VGA compatible controller: nVidia Corporation NV5M64 [RIVA TNT2 Model 64/Model 64 Pro] (rev 15)
02:01.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL-8139/8139C/8139C+ (rev 10)
02:03.0 Communication controller: Conexant Systems, Inc. HSF 56k HSFi Modem (rev 01)

The display is not recognised (acer AC711)

TIA

Kieran