Nikon D5000 Wireless Flash?

Currently I have a Nikon D5000 have the sb400, recently i purchased the 50mm 1.8 series e lense, and which i know that its an old lense and requires everything to be manually done. Along with External Metering, but my flash doesn't work. And i was curious if there's a wireless flash out that that would work with my camera and also this lens as well. Thank you.

Added (1). Yeah i saw the Yongnuo speedlight on youtube and noticed that its affordable, and alot more versatile and i like how you can chose the flash distance, so would this flash be operational in this case, bcuz i picked up 2 more older lenses that are just amazing and would be 1003420394 times better with flash. Please let me know bcuz if so i will sell my sb400 as soon as possible!

Unfortunately your camera can't work with Nikon's wireless system unless you buy a SU-800 to sit on your hot-shoe. But then your SB400 will not support wireless operation.

Your only solutions are to buy a SC29 10ft flash cable or buy a 3rd party (or SB900) flash that supports slave (manual) mode, and set it to flash off your camera's internal flash.

AWBoater is right. The SB400 does not support CLS.

An SB-600 would probably be the best choice.

Also, why not have a look at Yongnuo ( also known as YN ) flashes, they are relatively cheap manual flashguns that can be used as slaves. I recently puchased one and am currently experimenting with it.