Ram won't work together!

[steamy39]

HI everyone I'm new but need help.
 I've got a computer that has 256mb of sd ram & dicided to upgrade.
I used a crucial scan to find out I had 1 free slot & that my motherboard would go up to 1024mb. I bought 2 sticks of 512 from different sources which were secondhand.
We fitted both sticks & the computer was trying to start but wouldn't, so we removed 1 stick & it worked fine. So we remove that & tried the other one & it worked fine!! So we assumed it must have a faulty slot but we have tried both sticks in both slot & they work fine but they won't work together! Has enybody got any ideas the 512 upgrade has worked a treat but I'd love to get up to 1024. Do I need to buy 2 identical sticks???
                                      Regards.

[Dias de verano]

Yes you probably do need to get 2 identical sticks. It is very common for RAM of different spec to not work together.

[steamy39]

Thanks alot for yr help

[patio]

With the price of RAM dropping the way it is these days it makes sense to buy new RAM...the warranty is worth  the extra few bucks.