Can't see any startup choose when start laptop

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http://askubuntu.com – When, I try to install ubuntu 12.04 in different partition. After in compltation of my ubuntu installation. My laptop restart but i can't see any bootloader or start up choose what os i want to choose(windows or ubuntu) . After this i cant run my window 7 also, Onle blink _ sign appers on my blank back screen. So what can i do for run windows or ubuntu. After this again i try to install complete ubuntu via usb flash disk. but I have 400gb hard disk, in one drive /dev/sda4/ but have 3 partition in window after ubuntu installation c d e. How to recover my windows7. (HowTos)