My user id and pwd not working. If i use the capcha forget password link it shows "zenphoto_sendmail failed to send The Zenphoto information you requested to one or more recipients"

You will then have to use the troubleshooting guide's alternative means for recovering your password.

where will i find troubleshooting guide?

Ah, come on...

This what the BlueHost tech support sent me.

"there were some broken files in the zp-core folder. I renamed your old one to zp-core.brokena and replaced it and now the site is back up."

Since that day if i go to my site it shows up but my login ids dont work. Even reset pwd by means of CAPCHA doesnot send any email back to reset the pwd. If i go to my C-panel it does show two folders now 1) ZP-CORE 2) ZP-CORE.BROKEN

Please help.

I don't suppose you even tried the other means of resetting your password that the troubleshooting guide mentions? Give us a break. You have to actually do some effort in this support process. Unless you want to give me all your BlueHost credentials I can hardly fix this for you. (Even if you did, I would not!)