You must be using one of those cheap Odyssey/LiveTech/VIP/Zebronics PSU's.
I'm surprised your PSU's lasted 6 months. I wouldn't count on one of these to last 6 weeks.
I highly recommend only buying PSU's Teir 3 and above from this list PSU TEIR LIST As they have all been tested and certified. If you get one from the following list you should not have to worry about replacing your PSU for years, depending on which you buy. The PSU is the most stressed and needed component in a PC. never EVER buy a cheap PSU, always buy a good one, that way you will keep it for years and never have to replace it. Alot of cheaper PSUs are very dangerous, Not good for overclocking, can catch fire/smoke and can even kill your components in your PC.