I've also been having the same problem. I haven't tried these solutions, but I thought I would point out mine is also from DealExtreme just like everyone else's. Our problem seems to be different as ours will actually freeze when the DS is booting, so far for others I've just read about freezes when loading a ROM after the menu has loaded.
Might be worth avoiding DealExtreme over for this one... I got my original R4 from them years ago and it was fine, but these DSTTs might be faulty.