I would try taking EVERYTHING you can out - disconnect the DVD and so forth and then reinstalling. You can get this sort of problem when a connection is not 100% so that a device appears intermittently. The software checks whether the device is there and then the rest of the code assumes it is. A loose connection can make these assumptions invalid and lead to crashes.

A more depressing possibility: you say the RAM is new. It is possible you have damaged the socket or motherboard when you fitted it.