Replaced Pavilion Dv6000 MB, doesn't boot even after switching cpu of same specification

Sounds to me that your replacement motherboard is bad. Where did you get it?

From  retail supplier , not  a new board though

What I do when I replace dv6000 motherboards is lay the MB on the bench. Attach the CPU, heat sink, 1 RAM module, the power and switch.
Then I connect an external monitor, keyboard and mouse and I lay the hard drive in place and fire it up to make sure everything works before putting it all together.

I keep a spare power board on hand so I don't have to remove it.

Oh yeah, and I don't fool with used dv6000 MB's anymore. Good used ones are very rare.

This is the search I use to find new ones.
http://computers.shop.ebay.com/?_from=R40&_trksid=p3910.m570.l1313&_nkw=dv6000+motherboard+new&_sacat=58058

That sounds like another bad board to me as well. When will HP learn?

edbedb's suggestion about benchtesting the board before final installation is an excellent idea that can save you a lot of trouble and a lot of screwing/unscrewing. Just be that that the bench in question is in a static free environment as many times the damage static can cause is overplayed, but it is not something worth messing with as a risk factor.

After several attempts  of retrying  to boot  now I get  1 long beep and 2 short  but no display I even tried another set of new memory from another noteboook and have an external monitor attached.