Help - Cannot Start-up Even in Safe Mode

Several months ago we added 2GB of RAM and our Dell Dimension 4700 ran great.  All of a sudden we cannot get the computer to start up.  We get the Dell screen and then the Windows screen for just a short period of time before the BSOD.  We cannot start up in Safe Mode.  The Error message on the BSOD does not mention any drivers and the error messages are some times different when we try again.  A typical Error message is something like Stop: 0x0000007E (0x80000003,0x805C49B8, 0xBA4C32B4, 0xBA4C2FBO).   We do not know if this has anything to do with the memory upgrade since since the computer worked fine for two months.  Thoughts?