Amp affected by Cold?

In general, amps are not affected by cold weather.  It is possible, however, that if an amp (or any electronic device) is really frozen that rapid heating when it is first turned on can crack components and even the circuit board, especially if it is turned on at high volume levels.  The best thing when it is really cold is to turn your system on at very low volume and allow it to warm up slowly.  Slowly turn the volume up to normal listening levels over about a 15 minute time frame.

On the other hand, speakers can easily be and are often affected by very cold weather.  They have moving parts that are susceptible to freezing.  It is very common to shear off a voice coil, break a surround, or simply fry a VC electrically that is frozen in very cold weather.  Just like your muscles, everything in a loudspeaker stiffens up when it gets cold.  So again, the same advice as above, warm them up slowly for best results.

On yet another hand, your supposition that it may be your Lanzar amp could be the only problem.  In my book, Lanzar = crap.  It is very common for these things to go out at random times without warning.  They are boat anchors as far as I'm concerned.  The sooner you can replace it, the better off you will be.