No one has any idea what you mean by slightly damaged the motherboard box. I know for a fact that if the UPC code is missing from the box... that's an automatic refusal for return.
New merchandise may be exchanged or returned for refund with your original packing slip subject to the conditions listed below. Micro Center® reserves the right to decline any return or exchange where the product is not in "like-new" condition. "Like-new" means the complete product in the original carton with all equipment, packaging, warranties, manuals and accessories.