The ACT LED is hardware driven by the TXD signal of the PC connected to it. There is an issue with some Dell latitude laptops where the DC powersupply causes the TXD signal to go active. During this state, ProSoft Configuration Builder,hyperterminal, and other serial communications packages are unable to connect or use the serial port. Disconnect the external power cable from the laptopand check if the ACT LED goes inactive. If so, then communications should be restored.