One of the problems can be that your the Battery for BIOS does not work. To see if your Battery is good you have to check the Clock of your computer. You can do that by adjusting the time to a certain time or the right time and date. And then turn your computer off and if you come back later and the Time is at 12:00 AM and the date says 1989 or something like that then the battery of CMOS is bad.
If it is bad this might be the problem because when you install your modem, the program that installs it for you does all neccesary configuration and it is saved in BIOS settings.
Since your battery is not good. Everytime you will have the default settings on the computer and the configuration made by the program will be lost. and if that is you will lose the configuration. you just have to buy a new battery.
If that's not the problem then you might have to unlock BIOS if it is locked and the settings cannot be changed if it is locked.
If you find that BIOS is locked then you will need a Program called BIOS Killer you can go Yahoo and search a place to download. If you want i can email it to you. Just let me know
unforgiven060186@conectateya.com
Hope this helps you.