Im fairly new to home recording so this may sound stupid, but i have a 2 part question

I've just brought a second hand behringer B2 pro and reading that it needs phantom power i've got a USB to XLR lead that said it could power mics, will this be enough to make the mic work for recording, plan is to go mic > usb lead > laptop?

also as the cable hasn't arrived yet and the mic has i thought id put it through my amp (marshall mg hdfx if it makes any difference) to see how it sounds and cant seem to get any sound out of it, i tried the same set up with a cheap dynamic mic of mine and it worked fine, so the second part of my question is, is the mic broken or is it mearly that this set up is wrong for the mic and will work when used with phantom power

Appologies if this is basic stuff
It wont work with your guitar amp because you need phantom power to bring it to line level, which your guitar and amp are already at. As far as the usb cord, if it says it can power a condenser mic, then the answer is yes, it will work, if it doesn't however, it will probably still work but you'll lose a lot of the integrity of the original signal and it may sound like shit, but again, if it says it powers mics, then hope it does just that and you'll be fine
The b2 mic is a condenser mic, wich means it requires phantom power ( 48V). that why you're not getting any sound when you plug it in your amp.

I dont know about your cable thing but if it give 48 V it should work with your mic. Otherwise youll probly need a soundcard or mixer to power your microphone.
It's a condenser mic, you need like it said, phantom power to activate the pre amp in the mic and to magnetize between the 2 diaphragms. You can get phantom power in some mixer or audio interface. There's more detail here http://en.wikipedia.org/wiki/Phantom_power, but you can't get a condenser mic to works withour phantom power
The condenser mic won't run through your amp because it requires phantom power; the dynamic mic works on your amp because it does not. In theory that USB converter you have can provide power to the mic, but I wouldnt be surprise if it degrades the signal a little bit. Your best bet is to get an audio interface with good clean mic preamps that provide phantom power.

If you're interested in getting an interface, just post your budget, what youd like to record and you'll get plenty of recommendations.
Cheers guys, Great advice and good to know i've not been ripped off XD