What was the reason you wanted to know what type of RAM your computer has?
--- Was there a problem you were curious about?
--- When seating a memory stick properly the end holders should automatically snap into place; did that happen?
--- Are you sure the memory stick was put back in place with proper orientation?
How many memory sticks are in the computer?
--- If it has more than the one stick you removed and you did not touch any of the others, remove the one you had already removed and see if the computer starts
--- If the computer starts do not shut it down afterward
--- Go on-line to a memory chip company such as www.crucial.com. Have it scan your computer and it will report what memory sticks you need so you can replace the one you took out
If the computer has only one stick then buy a replacement stick
In either case make sure to handle the stick properly; do not touch the gold edges and ensure you are not creating and static
--- Usually when touching parts inside the computer use one hand to hold the frame to avoid creating static
Double check surrounding connections in the area you were working
--- Maybe it isn't a memory stick problem but another wire/connection became "loose"
Is it possible the computer already had problems and the memory stick issues are coincidental?