This can be for any number of reasons including weak signals from those stations, a poor antenna, or a defective tuner in the receiver.
Without more information I can't even make a guess as to which one is your problem.
Just because you used to be able to get some stations before they went digital it does not mean you will be able to receive them with the same antenna and a new digital tuner. This has been written by many people besides me on a number of DTV web sites. My blog about antennas is at SolidSignal.com, my blog article links page on my web site is at: http://cs.yrex.com/ke3fl/KarrasCorner.htm
Answers & Comments
This can be for any number of reasons including weak signals from those stations, a poor antenna, or a defective tuner in the receiver.
Without more information I can't even make a guess as to which one is your problem.
Just because you used to be able to get some stations before they went digital it does not mean you will be able to receive them with the same antenna and a new digital tuner. This has been written by many people besides me on a number of DTV web sites. My blog about antennas is at SolidSignal.com, my blog article links page on my web site is at: http://cs.yrex.com/ke3fl/KarrasCorner.htm
PhilK