PC not starting because of RAM chip

Hi there,

I hope someone can give me some more info on something I would like to know. Firstly, I have a old pc which had 1GB DDR2 RAM (one chip), after a while I bought a extra 1GB DDR2 RAM chip, inserted it and everything worked great.

Not to long after that I builded a complete new gaming pc from scratch. I didn't have enough money for RAM at the time so I simply took the extra RAM chip I bought for the old pc out of the old pc and inserted into the new pc.

Now for a lil while both pc's have been running with 1GB DDR2 each. Today I wanted to give my new pc more ram so I took out the old 1GB DDR2 chip from the old pc and inserted it into the new pc, after doing so the pc doesn't appear to fully start. The screen doesn't come on.

I then removed the chip I just inserted and tried booting again, this time it was a successful boot. After that I swapped the 2 chips still leaving just one in, tried booting and it didn't work, screen didn't come on. I then tried putting both chips back in again except this time I put them into each other's slots. Tried booting and no luck.

After this I put both chips into the old pc to test them, it started up fully picking up both. Both chips are fully working however the 1GB DDR2 chip from the old pc doesn't seem to want to work within the new pc, just the newer chip I bought afterwards works in it.

The chips aren't the same make so that is one possible thing that could be the cause, maybe the newer motherboard is just more sensitive to that. Could it be that the chips aren't the same speed or something?? o.O Any ideas on what the problem could be are more then welcome