I dont have any website to convert my music , so how can you help me for that kind of problem?

There are plenty of free software that will download from YouTube.
I use the following:
You put the URL of the video in the box, select the quality and the folder that you want to download to. Then select the format. It will always download the FLV video file, but if you select one of the convert options it will create it in that format too. There's one for MP3 too. You can delete the standard file later if you want.

YouTube Downloader

On Amazon and Walmart websites, these get just as many 1 star reviews as 5 star reviews. All kinds of various problems with them.
I suggest you exchange it for another one to see if that helps.

Open

MP3 players can only play music files in mp3 file format.
You can download mp3 music files from the Internet to your computer and then copy them to your MP3 player using the USB cable.
For your CD collection, you need to convert your CDs to mp3 music files onto your computer or download them from the Internet and then copy them to your MP3 player after you have connected the USB cable to the MP3 player and the computer.
You can do this using Windows Media player and Rip the CDs - Media Player will create a MP3 music file for each music track.
Click on this link for instruction on converting music files to mp3 file format :-
http://www.fixya.com/support/r5798418-creating_transferring_mp3_music_files

Why not change another kind of excellent video download tool?
I recommend you have a trial of Video Download Studio,
Video Download Studio is a powerful video downloader and converter tool which can help you download videos and free music from popular online social websites like YouTube, Metacafe, imeem, Break.com, Dailymotion, iVeoh, Yahoo video, Google video, MySpace, Vimeo, RuTube, Blip.tv etc. Supported Video Sharing websites. It also helps you convert online videos to all kinds of video and audio format like AVI, WMV, MPEG4, MP3, WMA which can be import to Windows Movie Maker or other mobile devise such as iPod, iPhone, PSP MP3 Player etc.
Get a free trial from http://www.downloadvideos-convert.com/download-videos-music
Hope it can help you more or less!

Depending on what kind of video if it's a youtube video u want u should try www.benderconverter.com that website should help u download any video from any website into any format just try to figure out wich format supports it

Why not try another excellent video converter to help you with this?
Video Download Studio is a powerful video downloader and converter tool which can help you download videos and free music from popular online social websites like YouTube, Metacafe, imeem, Break.com, Dailymotion, iVeoh, Yahoo video, Google video, MySpace, Vimeo, RuTube, Blip.tv etc. Supported Video Sharing websites. It also helps you convert online videos to all kinds of video and audio format like AVI, WMV, MPEG4, MP3, WMA which can be import to Windows Movie Maker or other mobile devise such as iPod, iPhone, PSP MP3 Player etc
Get a free trial from http://www.downloadvideos-convert.com/download-videos-music
Hope it can help you more or less!

Your friend is right in part, if you want to put music on your r4i you can, if you drop and drap the music you want onto your sdcard like you would games, you can keep them in mp3 form, i did this for my grandaughter, when i put them on the card i dropped them onto the moonshl folder, then when you turn the dsi on you go to the moonshl folder and you can find the music their and play it, when your friend said you have to convert to aac files thats if you put them on a sdcard on the side of the dsi insert them, if you do that you have to convert to aac, the dsi will not play mp3 files, but it will if you put them on the games card and drop them onto the moonshl folder, if you want to convert your files for the sdcard on the side of the dsi, what you have to do is download itunes if you have not allready, put the music you want to play on your nsi into a playlist on itunes, click on the song then click on where it says create aac version, then when you do that you will see itunes converting it, when you have done that with all the songs you want, right click on each track that itunes has converted and click on where it says show in windows explorer, then when you have all the songs in windows explorer folder drop and drag them all to your sdcard, then put the card into the side slot of your dsi, turn on your dsi, and find the sd menu and their you will find your music, hope this helps you.

you have to convert your files into .smv format. those are the only types os videos that the player will play. your music player should have come with a cd and that cd contains a program that will convert your videos into .smv format. if you dont have the cd, you can download the program from the trekstor official website.

Right click on song name, select properties to find out what kind of songs you have

Need to find an mp3 converter software from internet - they are probably illegal, and i don't know of any free ones