the external monitor is detected correctly and appears to work to a point, but then flickers off and back on randomly. It settles down to being mostly off. It does not appear to make any difference what resolution you select, from the "recommended" native monitor resolution right down to 800x600.
I've tried different VGA cable/monitor combos but to no avail (and I've proved that the monitors/cables work fine on other systems).
I am SURE it's a driver issue, since the external monitor works fine in SAFE MODE, then works fine with uninstalled 9300M GS driver, then got error with Dell's driver and Nvidia's drivers..
One odd thing I notice is that when I restart the machine with an external monitor plugged in the bios messages scroll past on the external display not the laptop's internal one. Even though in Windows I had not made the external display the primary one. This seems a little unusual.
I'm sorry to tell you this but this is a sign your nVidia 9300M GS GPU is on its way out. This is typical behavior for a faulty GPU chip. It usually happens the other way round - no more display on internal but working on external, but with yours it's no external. Same root issue tho.
The 9300M GS is from a defective series of chipsets by nvidia, manufactured between 2005 and 2009. A few years back nVidia got sued for the massive rate of failures of the 8400M and 8600M series of GPUs on laptops of all brands, and warranties were extended for all affected laptops. Unfortunately the 9300M GS was not covered, and the extended warranties are no longer offered anyway.
It is normal that the BIOS messages display on the external monitor. Most laptops are designed like that - so you can use an external monitor if you crack your laptop LCD. There are a few where you have to press a key combination to get the VGA output to work, but the vast majority have auto detection and will output to VGA first, when it is connected before power on.
kindly share your system service tag# to check present system config.