Tranny Will not drop into drive or reverse

Took my car out xmas morning and stopped at 7-11. Pulled out of my parking stall and put my car into drive, and the car went into "neutral", I was able to shift from park to call gears but the tranny did not engage the gear. Im getting no warning lights we have had the vehicle for about 2 weeks, and haven't noticed to much wrong, no grinding, no gear slippage or delays, We just had the clockspring changed which they disconnected the battery which I dont know if it has any impact on this issue with the computer, being that the car had been on the road for 3 days since that part is changed. For 3 days no issues. We have checked the tranny oil and needed to add 2 bottles was getting low, and was a darkish brown but did not detect any metal particles in the oil. As well we checked linkage and thats not an issue. I also read online that maby the filter needs replacing and if you let your engine run for 30 min in neutral that this would heat up the oil and make is thinner and see if you can shift gears, that didnt help. We are going to take it to a mechanic tomorrow but was hoping to see what else it could be before I walk in to the shop.