I started getting random Loading screen freezes now and then about a month ago, ejecting/inserting the cart (sometimes several tries :/) worked.
(I don't take the cart out when I swap MicroSD's, I carefully just eject the MicroSD itself and leave the cart in the system)
Well, today it finally started giving the constant Loading freeze no matter how many times I cycled the cart/etc. I figured it was the same 'death' that Tikker and others I've seen on the r4ds.net forums had, and was bummed. Cleaned the contacts...cleaned the pins in the Slot 1 as much as I dared from the slot opening, etc etc. No help...and it wasn't a problem with the MicroSD since it wouldn't give an SD/TF Error! - Can't Find SD/TF! - etc error when there was no card in.
I tried pressing the cart in while booting, and that worked most of the time...but you can't really use it while holding a cart in halfway though, so that was useless, but it did show the R4 actually worked.
...anyway, I just fixed it in a ghetto fashion. I made a shim out of a cut piece of printer/typing paper (folded, 4 paper-thicknesses worked...didn't want to bend the shielding or crack the cart or anything
), and placed it in between the R4 cart and the Slot 1 housing. The spacer/wedge/shim/whatever you want to call it goes on the label side of the cart...the opposite side to the pin edge, of course, in order to press the R4 towards the Slot's contacts a little bit more. Powered on, and it booted right up just like new, and has consistently over the last hour or so of MicroSD-swapping and testing to make sure it was working okay.
So yeah, if anyone still has this problem and still has their R4, just try this...hope it works for you too.