Memory problem after adding extra DIMM

I am having HP Compaq DX2200 laptop and I am trying to upgrade the Main Memory (RAM) from 1GB to 2GB. When I bought the RAM and fitted it properly in slot, the BIOS setup was showing main memory as 2GB. But it wasn't recognised in Windows. Then I upgraded my BIOS and now it shows CMOS checksum Error - Unsupported Memory Configuration. Power Off and Remove DIMM. Later I found that the Original DIMM was 667MHz and the new one I purchased was of 800MHz. Is there any trick so that I can have RAM of 2GB. PLease help me out.

Before using RAM of different frequencies, You should get the concept of it. If your mother-board has low FSB (Front Side Bus) speed, then highly clocked RAM wont do anything good. Suppose that your FSB can support upto 667 mhz, then even if you have 800mhz it will run at 667mhz because your motherboard supports upto 667 mhz. So its good if you replace the RAM of 800mhz by 667mhz, because according to me your motherboard can not support 800mhz.
Many people dont have much knowledge about this, so i suggest u to take 1GB RAM of 667mhz.

RAM is used for the execution of processes. More memory faster the speed. There is very little difference between DDR2-667 and DDR2-800. The DDR2-667 is CAS 4 and the DDR2-800 is CAS 5. I think your MotherBoard doesn't support 800 mzh memory, so it might have crashed down. Just buy the Memory of same frequency and try to boot your system again. I think there was no need to Upgrade your BIOS. You have totally messed up with your stuff. Try as i said and hope it will help You.

According to me it really doesn't matter which clock rate of RAM you buy because you are likely to not notice the difference. I would say go with the cheapest. I think its not always good idea to get what is latest. Higher Mhz is always better than lower Mhz, and lower latency is better than higher latency. However, always keep your RAM in groups of the same model. I think in your case you will have to check by putting 667MHz. If that wont work try to downgrade your BIOS. The Error told by you might have come because of your CMOS battery. Just check your CMOS battery once.