Why doesn't it print blue, but instead turns it red?

The printer won't print at all if there's an empty ink cartridge, (but a low magenta cartridge MIGHT be the problem.) It's probably either an issue with the color management settings or clogged print heads... so check the ink levels and also try running the print head cleaning routine (multiple times if it improves but doesn't go away with a single run). If the printer sits for too long without being used it tends to have problems with the ink drying out on the print heads and clogging them.

Good Luck.