Probably the simplest way Karen, is to start in "safe mode" then do a "system restore" to set the system at an earlier date when it was working properly
Is one of the bootup options "Recovery Console"? Try and do system restore from there. If you do not have the Recovery Console option, try and get someone elses Windows disc (same version as the one you are trying to start up). Ensure pc is switched off, put disc in and start pc up. Boot into Recovery Console.