How do i know if my alternator is gone?

My car will not start.. tries to turn over and just dont make it.we went out and installed a new starter and spark plugs.and the car will still not turn over?Last week we did a head gasket change.Well we changed all the gaskets that came in the kit. I was driving home and the oil light came on blinking and so i thought what we did .. did not work... so i out in some more oil. and it was fine for a few miles .. then it happened again so we pulled in a gas station and put more in.. so now we are 2 quarts over! Yesterday i thought we had to much oil so we drained it and put the normal amount in..and the car is still not turning over......any ideas...??