This will make my job obsolete as a BI person but ...

Add an identity column (surrogate key), and a Change_Type (price change, promo etc) to the renamed Prod_Hist (was called Promo_Prod) along with the natural keys (only really need the from date as these must be continuous from and to dates - more than one promo active does not make sense to me - sounds like a larger thing than product - we call it a bundle in telco - thats another discussion).

Use the TSQL Merge Statement as follows ...

For new (inserted) products you create a new Promo_Prod with no to date or largest date possible for the data type (means no expiry) and the current price. For changes to product price use merge to update old price's to date and insert new price from date with same to date and null for the to date. Same for promos changes. When orders are created they use the price in the Prod-Hist since it only exists there. There's a lot more to this for complex requirements but this is a good taste for a simple requirement around price and promo changes.

excuse my quick answer for spelling, clarity etc.