When Marcos walked into the room, we turned on the lights and yelled "Happy birthday!
What is your question?
When Marcos walked into the room, we turned on the lights and yelled "Happy birthday!"
It seems like you have provided a statement rather than a specific question. However, if you would like an analysis of the situation, it appears that Marcos walked into the room and was surprised with a birthday celebration. The lights were turned on and everyone yelled "Happy birthday!"
If you have any specific questions about this situation or anything else, feel free to ask!