According to this link, the memory of Compaq Evo N610c can be upgradable to 1024 mb.
Memory Upgrade for Compaq Evo N610C, the Compaq Evo N610C takes the PC2100 DDR SDRAM SODIMMs Memory Type, and comes installed with of Memory. You can upgrade your Compaq Evo N610C to up to a maximum of 1.0 GB Memory, the system has 2 sockets to install Memory, already with standard Memory installed. For best system performance use the maximum amount of allowed Memory per slot for your system. (Souce: http://www.memorystock.com/memory/CompaqEvoN610C.html
So you have to install 512mb memory module on each slot to make up 1024mb of memory.
Did you install 512mb memory module on each slot or did you just install 1GB memory module in one slot?
Try to go back to 256mb RAM and see if you will have the same blue screen error. If you did not receive any blue screen, try to add memory into it or just insert 512mb first and then oserve again if you will have the blue screen error.
You may also want to go to these links for other suggestions.