No bootable device showing

@arfatshaik73507 sounds like your computer can either not find / read the hard drive (or SSD) or the files on the drive are corrupted (OS failure). You need to try and access the BIOS on the computer and see if the BIOS can see your hard drive. If it does not it is most likely a failed drive. To repair that you would have to replace the drive.

If it can see the drive then it is most likely an issue with the MBR (OS failure). We need to know if this is a HDD or an SSD

To get into the BIOS just press F10 repeatedly at startup.