How much power supply do I need for my server, and could a shortage be causing my odd crashing?

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http://serverfault.com – I have 5 servers, all with similar hardware (i7, four 2tb 7200rpm drives, two 4tb 5400rpm drives, 430 watt power supply), and lately the machines have been freezing up. This has gotten worse in the last day or so, and I can't pinpoint any explanation. One recent change was adding the two 4tb hard drives. The crashes happen most often while running a large Hadoop job, so I was originally thinking the load was causing some issues, but last night one server just froze without any heavy load on the box (or so I think), other than HDFS (Hadoop's distributed file system) was probably rebalancing (HowTos)