[albee1952]

The 2 meter spikes are probably not the mic. That's just the voltage coming on and settling in(it would probably act the same with no mic connected). Absolutely try a new mic cable(you should always have a spare, anyway), and try another mic as well(even if you have to borrow one, or take the Rode to a local music store and test on any mixer). Things to consider:
1-The NT1A is a "budget" mic, so don't feel bad if it needs to be replaced.
2-Try a dynamic mic(everyone should have an SM57 on hand anyway) as they will work even if phantom power is dead.
3-You must use an XLR-XLR cable for phantom to work(phantom voltage does not connect to the quarter inch inputs).
4-phantom requires all 3 conductors of the XLR cable, while a dynamic mic may work fine with only pins 2&3 working
5-phantom is easy to test if you have a simple volt meter. set the meter to DC and a scale that covers at least 50 volts and then measure from pin 1 to pin 2, and again from pin 1 to pin 3. You should see the same voltage at both 2&3, and it might not be 48(could be anywhere from 30 to 50).