You can verify whether your power supply is an issue by estimating your power requirements. There are several calculators on-line that will ask for your hardware and then tell you the power requirements... so for 2 hard drives, 2 CD/DVD drives, this much memory, etc....
Compare that to your actual PSU and see where you stand. The PSU can't be too big... it just won't use the excess. It can be too small, however... were I building a machine, I wouldn't put in less than a 500watt PSU. But that's me...
Backups... good...
