NO bootable device found and unexpected store exception

some time my laptop stop working and  msg popup that NO BOOTABLE DEVICE FOUND or some time its showing that error- UNEXPECTED STORE EXCEPTION  when i restart it again it start working for sometime .....

I try to fix it so i have done following things

1) run diagnosis....no issue found with any component

2)change BIOS UEFI to LEGOS.....my system stop working and shows that no bios found so again i can change it back to UEFI

3)uninstall the Realtek usb 2.0 card reader driver .....issue not solved

4)disable all services after hiding Microsoft services.... issue not solved

plz..suggest any write way figure it out what problem is going on and how to solve it...