Why is your display in oblivion only in blue

Are you referring to the entire screen, or your character's "vision"? If so, then that means your character has some kind of Night Eye effect in use. This may be caused by taking some kind of night eye potion, casting a spell with a night eye effect, or wearing some kind of clothing with a night eye enchantment. The Night Eye affect gives your character the ability to see in te dark. Khajiit race players have this affect permanently, and it cannot be removed. If you are akhajiit player, the night eye effect shoudl wear off once it becomes light again/the sun comes back up. If you are not a khajiit player, try checking all the affects of your enchanted clothing to see if that is what is causing the blue vision. If none of this works and it turns out that your character is not experienncing the night eye affect, it sounds as though you have a technical problem on your hands which, unfortunately, I cannot help you with.