blacklight said:
how does bios get corrupted??
Take your pick - ESD, power surges, incorrect flashing procedures and many more that I can't really think of right now.

But those are pretty much the main reasons for a BIOS corruption, especially the last.
yehmeriidhain said:
Oh! c'mon Y update Bios it was there earlier in a second Bios expired or wat ..
yup its not shown in Boot Device list!!
Ok, so its not in the Boot Device list. But tell me something, is it showing under the Devices list in the BIOS along with the hard disk? Because its very unusual (not to mention, unheard of) for a BIOS to show the option as a regular device in the device list, but not in the Boot Device selection. Did you try soft-resetting the BIOS and auto-detecting the drives?