The 240 V. Is that on the power supply? If it is then we have just found your problem..
You definately need to go up to at least a 300, because those cards, like I mentioned earlier, are serious power hogs.
Just to make sure though.. (I don't know how much you know about computer hardware so please don't get offended by my description) The sticker that I am talking about would be on the side a a smaller box inside the computer that all the colored cords are coming out of. The largest number of that sticker (not including serial #s and the like) is probably the max output for that power supply.
Again, if we are talking about the same thing you can pick up a quality 300w power supply for about $25-$28 USD.
here's a link for a good one just to give you an idea of what I'm talking about.