I went to crucial to check my ram model and it gave me a PC2-5300, So I bought 2x1GB, couple of days later if arrived and I placed it in my computer which already have 2x1GB made by Samsung while the newer one is made by Micron. I checked my old ram and it stated PC2-4200. I started up and my computer doesn't boot but does a long beep sound repeating. I google the problem and it said memory/ram problem. Whats going on? I though newer rams were suppose to have backward capabilities.

There is backward compatibility...and there is compatibility between modules of differing speeds which are made by different manufacturers.

Have you tried each pair of modules...indivually (2 at a time, not all four)?

Running the PC5300 isn't going to do you very much good, if you have PC4200 installed and intended to add to it. Any RAM combination of modules (if compatible) will run at the slowest speed of any module installed. Your system/RAM clock will adjust downward automatically, unless you've modified the BIOS settings.

System manufacturer and model? If custom-built, motherboard manufacturer and model?

Louis

my computer model is m7747c here is the spec

http://h10025.www1.hp.com/ewfrf/wc/documen...product=3359917

how do I modified it?

http://h30434.www3.hp.com/psg/board/messag...message.id=3#M3

http://h10025.www1.hp.com/ewfrf/wc/documen...product=3359917

The HP specs say PC4200, most memory vendors say PC4200...except Crucial.

I'd install just the Crucial RAM and see if it boots/runs. If not, give Crucial a call asking for an RMA.

http://www.crucial.com/support/returns.aspx

Louis