When building a system up from new parts (or even old ones that have been laying around idle for a while), I've often had weird random problem behavior. Often it's just oxidation on the contacts, causing intermittent connections. Once I started adding/removing/replacing any edge-card connection devices (RAM modules, video cards, etc.) repeatedly up to six or eight times, which wipes off the oxidation on the contacts, I've had lots fewer new-machine issues.