Startup repair?!

Hi,
it's been about 1 year and a half that my Windows 7 system is running without any problems. But this morning I had a startup repair for the first time. I don't understand why it ran as yesterday evening when I shut down my computer, there was no problem whatsoever. So what could be the reasons why the Startup repair started?

I shut down my computer with an external HD connected but disconnected it when the computer was shut down. I hardly can see how it can be the reason as it's not the first time I did so but who knows.

Do you have a error code?

If you would like to
Check your ram.
http://www.sevenforums.com/tutorials/715-memory-diagnostics-tool.html?ltr=M
Memtest86+ - Advanced Memory Diagnostic Tool
Check your HD.
1) Boot DVD, & Press Shift+F10 (for command prompt)
2) Boot DVD, & http://www.sevenforums.com/tutorials/682-command-prompt-startup.html (for command prompt)
Open an command prompt.
In the command prompt, type chkdsk C: /f/x/r/v and press Enter.

http://www.sevenforums.com/tutorials/433-disk-check.html?ltr=D

http://www.sevenforums.com/tutorials/1538-sfc-scannow-command-system-file-checker.html?ltr=S
http://www.sevenforums.com/tutorials/96938-check-disk-chkdsk-read-event-viewer-log.html

Check the hard drive with the manufacturer's diagnostic tools.
Hard Drive Diagnostics Tools and Utilities (Storage) - TACKtech Corp.
HD Diagnostic

I didn't get an error code, but there may be a log about that somewhere (where?).

You're suggesting to boot (on the Win7 DVD I guess) to do a check disk, but why not do so in Windows directly?

You can do from DVD or Windows desktop.