Hello,
Try CTRL + ALT + T to check whether invisible prims, this will help you with seeing them in red.
To return to normal view, type CTRL + ALT + T again... I hope it would work out.
To reset (or maybe so to speak) would be possible provided that you have a private region; if it applies to you, go pls to World -> Region/Estate and you'll see there "Restart Region" option. Another possibiliy would be to return all objects if the land is yours or you have such a right... But pls check first CTRL ALT T combination...
Cheers...