Which R4 do you have very specifically? If it is an original, try to back up and reformat the MicroSD card. Pictures help if you can't get enough info from the card. Note: If it says Ultra, SDHC, R4i, etc., it is not an original.
There's your problem, you have a clone. http://forum.romulation.net/index.php?topic=43005.0 Refer to the bottom most spoiler in the first post for the best carts to replace that with. I wouldn't recommend pretty much any R4 clones for use, as they tend to have poor compatibility.
Update to your latest firmware and see if you can possibly get YSMenu to work on it. Just find a tutorial on getting YSMenu to work on clones. Wood R4 for clones is very unreliable and sucks. I recommend a new cart, as R4 Ultra is just a very poor clone overall. http://forum.romulation.net/index.php?topic=36273.0 Should be the tutorial you need.
r4 originals are only 8$ on a us website including shipping. On a chinese website if youw ant to wait weeks for shipping they are much less.
Trust me, you don't want to buy an R4 Original if you're getting a replacement. Although a good cart, that 2gb limit can be crippling to some. On top of that, it lacks the features of better carts. If he chose to get a new one, I would go with the Acekard2i, Supercard DSTwo, or the CycloDS. The CycloDS is the absolute best for DS phat and DSlite systems, but it is also the most costly cart available.
If that was how everybody thought, everybody would just have a 512mb card and call it good. If you're getting a new cart, the ones I listed are the best way to go.
