*Download a copy of Memtest86 and burn the ISO to a CD using Iso Recorder or another ISO burning program. Memtest86+ - Advanced Memory Diagnostic Tool
*Boot from the CD, and leave it running for at least 5 or 6 passes.
Just remember, any time Memtest reports errors, it can be either bad RAM or a bad motherboard slot.
Test the sticks individually, and if you find a good one, test it in all slots.
Any errors are indicative of a memory problem.
If a known good stick fails in a motherboard slot it is probably the slot.