Hi
Have you tried another VGA cable or only this one?
In your case I would try to update the display driver and BIOS. Both updates you can find on the Toshiba website:
http://eu.computers.toshiba-europe.com => Support & Downloads => Download Drivers
Before you update the display driver, remove the old version first. Then restart the notebook and install the new one.
And before you install the newest BIOS you should close all running application and also disable the firewall and antivirus program!!
Generally if you connect the notebook to a external monitor you should connect the devices first. Then start the external display and after this the notebook.
On my Satellite L300 I don’t have problems with my external monitor.
Greets