If the motherboard is a DP35DP, then 3 beeps is a memory error, as @abrsvc pointed out. The beep codes for your motherboard, what they mean, and what you can do about them can be found on a chart at:
[link|https://www.intel.com/content/www/us/en/support/articles/000005473/boards-and-kits.html|https://www.intel.com/content/www/us/en/support/articles/000005473/boards-and-kits.html]