00 blazer 4dr......as of last night...the brake light is on..pedal feels a little spongy while driving... when off the pedal hardens right up....dont see any leaks and fluid is not missing from master cylinder....could this be due to something frozen from ice/snow?

 

When is the last time you flush the old brake fluid out?

 

It's always possible that the cold/snow has caused an issue. But it could just be a normal failure as well.
If you havn't done any brake work lately, and your fluid levels are good with no leaks then it is time to start checking the vacuum and electrical connectors on your master cyl and abs system. (I'll assume for the moment that all pads are good and there is no pulling indicating a bad caliper)

The main vac line from the intake to the master cyl should be checked first.