|"i get 3 beeps at startup"|
This is no "3 beep" beep code for the Dimension 9100. The codes are listed at the Dell site. There are also diagnostic lights that you should be checking. It can all be found here:
Also from the above site:
"If the power light is blinking amber, the computer is receiving electrical power, but an internal power problem might exist.
Ensure that the voltage selection switch is set to match the AC power at your location (if applicable)."