1) The easiest way to deal with the "point melt" is to add part cooling.
2) When using different filaments (ABS, PLA, Nylon, etc.) you need to make sure you purge the hot end at slightly higher temps then the highest filament temperature. You want all the old filament out if possible.
2b) The drive gear on the extruder motor may be clogged up with filament, not allowing it to grab the filament. It's a common problem when first starting out and having the bed slightly to close to the nozzle (some cheap filament can also cause this).