Ok i only found this out earlier today and it does work as I tried it.
this is how to remove a boot string that does not work (Ibased on the fact you have a dualboot os and want it to be single boot again as the other os dont want to work)
heres what you need to do
right click my computer - go to properties - go to advanced - go to startup and recovery - go to settings - go to default operating systems- highlight the choice you wish to delete - click edit (it comes up in a notepad document) - hughlight all text and press delete. save as boot1.ini.
click ok
restart your PC. hopefully this will work and only the one os will load. if not then re follow the above steps.