Error: Could not open the sketch

Yesterday, I downloaded Arduino Nightly for windows.......... I installed it, and then tried to open an .INO file but couldn't because it said "Could not open the sketch" What should I do??

N.B. I know absolutely nothing about arduino, so if its a dumb question please dont laugh...

the "nightly" version is BETA and as such subject to bugs or other unspecified faults and you use at your own risk.

Version 1.6.12 is actually quite stable and I would suggest fully remove the nightly and install a regular version.

I would also refer you here for more concise removal instructions