REW sweep on mid/hi, limit Hz?

The voltage setting in my REW seems locked at 1.00v. Through my laptop headphone out Windows volume set to 100pc and it all goes through my pre/power amp and I have the volume about 65pc so REW tells me the level is 'OK'. I'm never quite sure what I should be doing here apart from turning my preamp volume until the level test gives me the OK.!