Can be many sources for that problem. Is the power indicator still light up?

If its still under warranty then contact the shop where you bought the monitor from.

This post has been edited by lex: Jul 8 2013, 12:12 AM

Please post pictures of both adapters, the original and the replacement. The most important part is the label. You could have eventually burned/fried out your monitor's internal power regulators and components by using a higher voltage power supply...

Does it happen from cold start also? Have you tried using the monitor on another machine?

White screen plus vertical lines symptoms indicates LCD panel problem (Tcon board failure) and usually have to replace the whole LCD panel. Looks like its going to be RMA again, and hopefully not deliver another bad apple.

That depends, sometimes they have another unit with them (for another customer) which can be exchanged (and have to notify Dell himself as well). Should have quickly test/check the monitor first before the delivery guy left...