help... my amp stoped working...

[marrstians]

i found one problem... i was checking a few of the resistors, the 470ohm ones that connect to my tubes and they were fine, but there is another one a little down the chain that looks the same, the rectangular ceramic type, and i'm not getting any ohm reading from it... now the question is, if that resistor has gone out why did it and what else should be considered before replacing it?