Would someone please tell me what is the deal with certain DDR memory and some machines?

I caught a glimpse of an IBM webpage which states:
"Symptom
After installing a new memory option or FRU, the system hangs in POST with no video, memory error beeps, memory error message, or the system boots up showing lesser memory."

My system doesn't even boot, it does the no video, error beeps and that's it.

I just bought this 2x 512mb DDR 266Mhz, CL2.5, ECC (from Ebay) for my son's computer and it just won't work.

What can I do?

What can I do?

make sure you computer take the type of ram you are buying ,especially on E-Bay .maybe your laptop doesn't take, CL2.5, ECC ram maybe it take non ecc ram.

ECC is Short for Error-Correcting Code ,usually used in servers i think ,because it was more expensive ,but works for me in some Dell,IBM and Compaq machines i've put it in even though they originally had non ecc in them .

what is your computer make and model number ,what make/model # is the motherboard if you know it

It's a HP Pavillion 513N.

It's a HP Pavillion 513N.

if you put that into google.com ,you will find info on the ram it needs .i am only guessing but i thin it may need to be"non ecc"