alt+ctrl+del only works if ur computer actually boot up to desktop. when u enter those key combo ur computer restart in POST boot.
these problem can be cause by alot of things. corrupt MBR, boot sector, missing loader file, even a bad sata/ide connections. try using the windows that you use to install and use the recovery utilities or using the command prompt from the recovery to write a new boot sector or MBR. if all else fail put ur HDD onto another computer and back up any files and re-install windows.
hope someone else in the forum with more experience can help you.