Maybe the external monitor is being detected as a 2nd display and extending the screen. You'll need to open your display preferences (option+f1) and change your primary display or enable mirroring.
This page shows 512MB RAM: http://www.mrmemory.co.uk/memory-ram-upgrades/model/Toshiba~Satellite~S1000-Z2
Two separate Toshiba forum posts have stated 1GB in 512MB increments can be installed.
Continually press F8 on your keyboard after pressing your computer's power button and when you see the Advanced Boot Options screen, select "Safe Mode with Networking". Upon successful boot you will be able to fix your errors and connect to the web.