My xps 18 wouldn't start, all I had was a flashing white light next to the power button but the pc wouldn't start up, even if I held down the power button it just kept flashing white and had no screen activity at all, but I have a solution!
Basically you need to disconnect the batteries, which are unfortunately inside so it requires removing the back cover, but it's not hard at all. (Obviously this will void your warenty so do at your own risk, mine was well beyond free help)
So as described in previous fix, you only need to do stage 1,2 &3 to get back cover off, then just lift up the black lining to expose the battery connections see pics (is a bit easier if you remove the 2 screws holding the small middle circuit board in but you can manage without doing that) Main one is the black cable and smaller one has the black and red wires going into it... So disconnect these with the tool, wait a few mins then reconnect. I tried starting it again and it came up with a time error message but I skipped passed this by hitting F1 as prompted and it took a little longer but booted up as normal.
Hope this helps!
Don't be put off, it's a simple fix, just can't offer any advice as to why it got stuck like that in the first place!