I have a HP Pavillion DV 2000 laptop with me. When i boot my system it gives 1 long beep followed by two short beeps and the system doesnt boot. I am not sure as what to do. Can someone help me here?

Have a look here

1 long beep followed by two short beeps is usually indicative of a failed/failing display adapter. On something as.... rustic as your dv2000 it can be fixed.... but probably would see better value from just replacing the unit.

I found some info on a forum, it says the 1 long and 2 short beeps is a problem with the graphics chip. You may need a replacement motherboard.
Check this post out
http://www.computing.net/answers/hardware/1-long-2-short-beeps-hp-laptop-/52894.html

Did you upgraded your BIOS after you have changed the MB?
Did you install memory ? if yes check if it was compatible.Check Beep codes from net search.
You may use two similar but different memory for a short time but end of it, you will get this beeps. Check it by removing one memory each time and try the laptop, Make sure in process time, remove the battery and plug off power, otherwise you will demage the MB.
IF NOT you need to obtain (Or if you have ) OEM CD or order from HP to reload programs,
Mean time I also suggest, Remove the hardisk and with a niddle try to bring springs on from Hardisk Caddy connector. Do Not know how to do it? See techy.
Goodluck
JMC

try buying a new battery

DEAR,

PL SEND INFORMATION OF BEEPS SOUND.
HOW CAN BEEP GENERATE .CONTINUOUS OR ONE BY ONE AND HOW TIMES.

IF U ARE GOING TO HP SITE CUSTOMER SUPPORT THAT GIVES PROPER SOLUTION FOR THAT.

That indicates a video problem. You will probably have to replace the motherboard. 

Hi...
I had the same problem...
The solution is only temporary and you will have to reapply it after around 5 to 6 boots cuz it'll just happen again (the beep syndrome).

Just heat up the laptop by turning it on and covering its air vents with your hands.

Then after you hear the beeps turn it off.
Turn the laptop on again and immediately turn it over upside down with the lid closed ofcoarse (simply put it on its back).Hopefully you wont hear the beeps and when you open up the laptop lcd...voila display.

I have just experienced same p[roblem with my Pavillion laptop. Seems to be a graphics card problem. (Hp have issued extended warranties to cover this problem, which is apparently quite common in the pavillion range?)
I have had to send my machine back to HP to fix it. gah.

system is on but no display. yes i did heard sound 3 beep sound from the motherboards.