Can't boot Windows 7 after El Capitan installation

I have had Windows 7 with Bootcamp on my 2009 MacBook for a few years.

I just tried booting to it after upgrading to El Capitan and got the error message that I need to insert a bootable disc to startup. But, I'm never gotten this message before. And I can't find my original Windows 7 disc anywhere.

I've reset the PRAM and SMU

I recently upgraded to El Capitan, but the could have been happening in Yosemite as well, since I never used it in Yosemite.

As an aside, in case anybody knows, Mail will now download all messages overtime I launch it or even bring it to a forward window, even though I have it set to download manually. Any ideas on that?