a friend has a computer that worked and he changed to a different monitor and it did not start up correctly so he switched back to the original monitor and that did not work what can he do to fix this problem. his computer will not start up in windows it did before he changed the monitor he did not remove any thing such as programs he just unhooked one monitor and hooked up another one and then switched them back it had started up with windows 98 i have the cd but when i put the cd in and turn the computer on it says invalid system disk any help would be appreciated
