be a graphics card problem, try uninstalling drivers through your device manager(right click my computer>properties>hardware tab>device manager)and click the '+' sign on click and uninstal.
Reboot and allow windows to find hardware and drivers again.
Other suggestion is normally, more...
Acer TravelMate 506DX PC Notebook - Troubleshooting
Replacing a harddrive is simple, remember everything on a computer play. Remove the old harddrive and find a suitable replacement, it should snap right more...
Acer TravelMate 506DX PC Notebook - Troubleshooting