Phone locking and screen changing to colours

[Kelley Hickey]

Hi all. Having a problem with my desire eye. It's only 4 months old. For the past two days, while idle, browsing online or making calls, an alarm starts and the screen changes to different colours then it changes to my password lock screen. I've turned off all notifications incase it's coming from an app, but i have not downloaded any new app recently. It's really frustrating me now. I'm not very technical minded but have searched and searched online for an answer to this and can't find anything. Has anyone any ideas what might be causing this?