First I had Windows 7, Windows 8 and Ubuntu 12.04 installed side by side as triple boot.
Ubuntu Boot Manager was the primary one. Then I deleted the Windows 8 part and upgraded my Windows 7 to Windows 8.
Now when I boot in my system, I don't get the Ubuntu boot manager at all and directly boot into Windows 8.
Moreover, the partitions of Ubuntu were of ext4 format, so I can't even access those. And to top it all, now when I make a flashable Ubuntu in a pendrive and try to boot from it, it says no OS found.