Ubuntu Not Boot Loader Vanished.

Hello,

My PC Specs are in Signature.

I had Win 7 SP1 Installed on the SSD.
Then Installed latest Ubuntu Version. Worked fine for 2-3 weeks then the boot loader vanished.
System boots in Win 7 Directly.

I have the boot Disc with me. Kindly let me know how to fix and What may have caused the issue?