One way to avoid all this shit, buy a decent PSU from that start.
A "400 watt" PSU is very rarely that, unless its cost a decent amount of money. My mums PC (my old one) is running on a 400w Antec TruePower PSU, and it has been 100% over the years it been used, even when I was creasing it with intense voltages for extreme overclocking of everything, had 3 180GXP hard drives installed, Radeon 9800Pro, a Barton Athlon 3200+ overclocked clocked at 2450Mhz (probably around 4000PR) on 1.75v, 1.5GB of OCZ PC3200 ULL Rev 3.2 RAM (3x 512MB running at 464Mhz 2T 2T 2T 6T 1T @ 2.85v) along with numerous cold cathodes and 6 fans, all running LED's in,, 2 rear extraction fans, an Asus iPanel Deluxe, 2 CDRW's, 1 DVDRW etc...
The power draw must have been... well stupid, let just say before I bought my 400w, I was running on a "550w" PSU low end PSU (I think it cost about £35), and it just couldnt handle the load, it died within weeks of installing the Barton and RV360, and when I put a supposed "400" in until the Antec 400w was delivered, and it took literally 10 seconds before it went bang and smoked haha. I was lucky not to frazzle the entire PC to be honest!!
The Antec cost me £68, but was worth every penny, the 400w rating was actual power supply, not peak power like a lot of PSU's quote, that 550w I had running probably couldnt provide more then 300w sustained. To this day, the PC is still running most of that crap, and the PSU is still doing me (well me mum now) proud!
You have to consider the fact that buying a high end PSU, you get an almost true 12v supply across 3 (yes 3 lol) rails (like around 11.9v instead of the under 11 volts cheap ones max out at, which can cause your PC to randomly reboot), they will be far quieter then low end competitors, and they have circuitry protection features not found on cheap PSU's such as SCP, OVP, OPP and UVP protection, as well as dual circuitry to ensure redunandcy.
I say it again and again to people, dont skimp on the PSU, its the thing that puts the juice into your PC, if it does it wrong, your fooked, and its easy to overload and burn out cheap ones, which can also lead to burn outs on your hardware as they dont have circuitry protection on them.