ACER ASPIRE 3003WLMi Black screen on start up since memory upgrade.

[stormrogue]

My laptop was running really slow so I upgraded the memory from 512mb (2 x 256Mb sticks) to the max recommended 2Gb (2 x 1Gb sticks) and while it is a lot quicker now when I switch the laptop on it runs through the Os screen then just goes black I then have power down then start using last known good configuration settings and it comes on and works fine . Any ideas why?
The memory is showing as 2gb in the system info so I am sure that they are ok and I have switched them round into the different slots but no different , although if I revert back to the original memory the problem does not occur.