Issue: I'm no longer able to connect my gps to the serial port on my computer. The gps and serial cable have both been checked on other machines and they are not the problem. The device manager says the com1 port is working fine and that there are no conflicts. Thus, I have run out of ideas. I don't use a PDA or any type of hotsync program and I use a cable modem on the outside of the machine. The only thing I've ever used the physical serial port for is the gps.

I've read that some other program may be somehow blocking the port or using the IRQ but I'm not sure how to find out for sure.

Does anyone have any ideas??

Make sure COM 1 is enabled in BIOS.
Next, remove COM 1 from Device Manager, restart the computer, and let Windows reinstall its drivers.
Then, uninstall the GPS software in Control Panel/Add-Remove Programs, and reinstall it.

If no luck, then double click on Computer in Device Manager, check the IRQ circle, and check if COM 1 is sharing its IRQ with another device(It's ok if COM 1 is sharing its IRQ with 'IRQ Holder for PCI Steering').
If it's sharing its IRQ, then close the 'Computer Properties' window, double click on COM 1(or on the other device that's sharing the IRQ) in the Device Manager list, click Resources, uncheck 'Use automatic settings', select a different Basic Configuration, and see if it uses a different IRQ.
If none of the Basic Config's use an IRQ that's different from the one that's used in the orig. Basic Conf., then click on 'Interrupt Request' in the box to highlight it, click the 'Change Setting' button, and select an IRQ that's not being used by any other device.

If no luck, try another serial port(COM 2) if one exists and it's available. Also, make sure it's enabled in BIOS.

If that does not work or if you do not have a 2nd serial port, then it's possible that your serial port is bad.