I complained in my last post that ever since we converted Windows 7 to use BitLocker, my laptop has had problems in dual-booting. It seems clear that BitLocker and TPM require that every step in the boot process is controlled. Generally, that's a good idea for security. But in practice, it's a pain.
If something changes (say, the MBR gets updated by GRUB?) then TPM shuts off, and I need to enter a very long BitLocker key just to boot Windows.
That wasn't going to work for me. I guess Windows doesn't like to play nice with other systems. I don't boot Windows very often, but I'd rather not have to type in that long key every time.
I asked you for help, and got several helpful suggestions. Thanks! I liked one in particular: put GRUB on a USB fob drive. The simplest solutions are usually best. And I happen to have a small 32MB USB fob drive that I'm not using.
So, a little fiddling around, and I now have a bootable "GRUB" fob drive. When I want to boot Linux on my laptop, I just use the USB fob drive when I boot (I can take it out once Linux has started booting.) Easy! When I want to boot into Windows, I take the fob drive out of my computer, and boot from the hard drive.
But the most important part: I haven't had any problems in the last month, since I did this.
If you want to do this on your multi-boot system, you can google the steps needed to set up GRUB on a USB fob drive. But of course, it's far easier to just do this at install-time. At least with Fedora Linux, there's an option when you install to select where to write the boot loader.