I've seen too many people here with problems like this, who claim to be doing everything right, and still their new pi won't boot or won't boot consistently and perhaps even randomly corrupts the SD card. I don't believe they are all fools or liars. There are apparently 40,000 pis a week being made, and we get a question like this at least once every week or so, I think.
A while ago I ran across this thread, where someone claims:
Recently I purchased a Raspberry board labeled Made in China and I have already one board labeled Made in UK. [...] My old SD card image used for Raspberry Pi is not working with the new one.
If a card works in one rev. A pi but not in another, the second pi is broken.
Here's an interesting article:
production of the Raspberry Pi started in China back at the start of 2012, but has been gradually moving to Wales since last September
That was written early this spring, so "September" is September 2012. I know nothing about manufacturing electronics, but it seems to me arranging production in one place and then moving it across the world eight months later is not something a distributor does because they suddenly think, "Oh Of course, it wouldcould be nice to make them in England instead". They dofaulty anyway, even if it because there is a serious problem and they are abandoning the supplier.
That said, I have a made in China pi and it's fine (I believe it runs slightly undervoltage,1 but I have not had any real problems in 6 months of light but constant use). They can't all be bad after all.
So, if your pi says "Made in China" on the top where the SD card is, maybe it's faultyUK. The Chinese ones (also, the English oneswhich are no longer being produced) have a powder blue audioblack headphone jack, the ChineseUK ones are black). Of course, it could be faulty anyway, even if it is made in Englandpowder blue.
There is so much material already online about creating and using the SD card -- and it is very simple -- I do not see a point in repeating it here. If it doesn't work, it doesn't work.
You could obviously try another SD card to rule that out, etc. The way I would deal with this, if you decide it is the pi, and you can afford the $50, is to order another one, possibly from a distributor that only does the British ones (Farnell/Element 14). If you can't get either of them to work, either you are really unlucky or doing something wrong. But if one works and the other doesn't, you have a pretty good claim to send one of them back.
1 Testing with 2 different multimeters and using a variety of power supplies from 1 to 3.8 A, including a 2 A apple ipad charger other people have recommended for use with the pi, I cannot get more than 4.85V with no load attached to the pi itself.