Try it without the stick you pulled out. Just that other 512MB and hope it works.
I have Dell inspiron 6000 with 1GB ram(512 + 512).I bought a compatable 1GB (Kingston) one ram and tried to replace one 512 MB ram. But my laptop stop working.It automatically switch off after capslock indicator blinks for 10 times.I tried to put old RAM back but my laptop is still not working.
Please suggest some fix for this problem.