Windows boot manager BSOD AFTER UPDATE

[zVERON PLAYz]

The laptop came with win 7 but then my friend upgraded it to 8.1 pro and it worked fine for 5+ years yesterday I was trying to make ms store work again and it leads to turning on the windows update. After the shutdown and  now I opened it and it won't work .BUT THE WEIRD thing is this only affects the windows fast mode (in os selection which was my default os) I can still use 8.1 os normally but it blue screens frequently while playing games  (an old issue which the fast mode didnt have ) .Can anyone help me fix this (CHECK THE PICTURE BELOW)

[intelamdallthemisnice]

you should try rebuilding the bcd by opening system repair, then in the command prompt type bootrec/rebuildbcd.

If that doesn't work you should probably reinstall windows