"BOOTMGR is missing" message on Dell XPS 13

Hi guys,

Just bought a Dell XPS 13 (L321X model) for my wife. I made the initial setup for Windows 7, then started a Windows Update process. Turned the laptop at the end, and next day I got a "BOOTMGR is missing. Press Ctrl+Alt+Del to restart" message. I didn't format Recovery Partition, so it should be as factory default.

I read all possible posts on Dell's site, and followed the advices from http://support.dell.com/support/topics/global.aspx/support/kcs/document?&docid=DSN_353562&isLegacy=true link. Unfortunately, I just cannot access Advanced Boot Options by repeatedly pressing F8 after Dell logo. I tried Ctrl+F11 as well, but with the same lack of results. Hardware diagnosis (available by pressing F12 after the logo) revealed no problem.

Please help me to solve this issue, because I never faced something like this in 20 years of experience as a Software Engineer. I do not want to manually reinstall Windows, at least not before getting your opinions.

Thank you in advance!