Praveen,
What version of CA PM are you using? The reason I am asking is that there was a bug relating to the poller configuration (PCC) that caused some metric families to drop out of the PCC and it stops effectively collecting data. This was resolved in 3.6 I believe.
As far as rediscovering in bulk, there is no "entire environment" option like there was in eHealth. If you want to rediscover everything you would need to set up a discover profile to do so.
Troy