did you install anything before that happened?
probably a corrupted file/program
for the msconfig, you set the timeout: to 30 seconds or less?
try this also
right click My Computer, go to properties
go to Advanced
go to Startup and Recovery
change the time of display list of operating systems
but im pretty sure its probably a program that is causing it
run adware and spyware programs, anti-virus also
professor at your service