I would also look at cleaning up and defragmenting your hard drive. Empty your systems trash can. Then check that you have your computer OS fully updated and update your Nikon software. You might want to check and adjust your systems virtual memory.
What brand of computer? What processor model, clock speed, and how many cores are you using? What OS are you running? What is the amount of RAM memory installed? What size is your virtual memory set at? What is the amount of free disk space that you have?