Do you still have your dial-up modem connected? If so it may be trying to dial out for some reason. Though this would not affect your broadband in a direct way it may cause a software conflict in your PC that will cause your broadband modem to drop the connection.
If you still have an internal modem and it's connected to the phone line, try disconnecting it for a while and see if this cures the problem. If it does, then please post back and someone will help further with advice of settings if you wish to keep both. j.
Probably best not to go into your BIOS unless you feel reasonably sure of your way round. If you still want to have a look, then when you reboot your PC, keep tapping the Del. key on your keyboard. This will take you to the BIOS screen.
This is an area where you make changes to your PC hardware, if you change something that you shouldn't, you may leave yourself with a PC that won't boot-up. If you do go into the BIOS, your mouse will usually not work and you use the Up/Down/Left/Right keys to move about. Your enter key for yes, and Escape key for No.
After having a look round, press the escape key to exit, you will see a choice of options on the screen.
If you have made any changes and are sure of them, choose "Exit with save" otherwise choose "Exit without saving" Your PC will then carry on loading windows as normal.
Coming back to your dial-up modem, if the phone line is connected to it, then just disconnect the lead from the modem itself, this will be sufficient to see if this is causing the problem. Try this first and let us know how you get on. Regards. j.