I have a Gigabyte GA-P31-DS3L motherboard with 2x1GB of DDR2 667 RAM. I recently bought another 2x1GB DDR2 PC2-5300 667 (not sure if my older couple of cards is PC2-5300 but I don't think that it matters). I tried to install the newer couple with the old one (4GB) (I have 4 slots) but it froze at the first screen where you can see all the hotkeys to the bios setup/qflash/etc. I thought that the newer couple might be broken, so I removed the older one and booted up the PC. Everything launched normally. I tried installing a single card out of the old couple with the new couple (3GB) and I had the same problem as before. I tried using only one of the old cards and one of the new cards (2GB) to see if maybe there's a problem with the two types together but the PC launched normally in that situation too. I don't think that this is a problem with my power supply, as I also recently bought a new GPU that uses less power (55 Watts instead of 95) and all of the cards seem to be working fine, so are all of the slots. What could be the problem? I tried updating the BIOS to the latest version (F10a) but it didn't help.
Yeah, head into the BIOS and make sure timings are correct for both the old and new memory. Its best not to mix and match memory sticks as far as manufacturers and specs go. Increasing the voltage may help though, I would try that.
I wouldn't go more than 1.9V. What are the RAMs models?
http://i.imgur.com/ygQ6t.jpg?1 here's a picture of the two types. The older one is at the top. Also, I'm at +0.4V and I can see that the maximum I can go for is +0.7V. It still freezes on the first screen.
The new sticks, being from Samsung, are of much higher quality, unless they were damaged by static electricity through careless handling. I would be suspicious of the older sticks since they're not only from A-Data but also made from generic chips, as indicated by the A-Data markings on them. It's possible even the circuit board of the A-Data is inferior and distorts the signals excessively.
Most BIOSes slow the memory timings when more sticks are installed, to compensate for the extra load on the signal lines, but the amount of compensation may not be enough, especially for low quality memory.