As advised I am asking here about my problem. After upgrade to ubuntu 14.04 I can't boot in windows 8.1. Right away after upgrade I noticed that few of my previous options are missing in grub. Then I tried booting in ubuntu and it works. But booting windows doesn't. I only get error reading file for less than a second and than it returns me back in grub. I tried boot-repair with live cd in ubuntu 13.10 as advised. It ran through and it give me this http://paste.ubuntu.com/7299246/. I would be really grateful if someone would check it and tell me if something is wrong. Or give some advice.
Boot into Ubuntu 14.04 and try updating Grub
That will check for the other OS that are installed in your machine and updates grub then reboot to see if it worked
If that did not work then you have to repair your windows boot-loader first and then re-install grub
for windows boot loader
=> u need a windows 8 repair disc or windows 8 live usb or live cd
boot from any of the above windows disc and go to
Repair=>System Recovery Options=>command prompt
type the following two commands in cmd exactly
Bootrec/fixmbr 'press enter'
Bootrec/fixboot 'press enter'
now reboot u can see windows boot loader again
Now back to grub boot loader
=> u need ubuntu live usb and use " load ubuntu without install" then install boot-repair and repair grub u can see it in this how it is done https://help.ubuntu.com/community/Boot-Repair
if u install windows boot loader u can create a ubutnu live usb in windows using unetbootin(in case if u have a single pendrive currently)
i hope this will solve ur problem