I had a similar problem on my S710 and couldn’t locate the file omap850_sdhc_mux.dll in windows directory for the renaming solution.
But then I found another solution from one MS forum. Change the ‘Home Screen’ layout to Windows Simple, colour scheme & background image to default. Then it boots OK, consistently. (If the SD recognized and being mounted as ‘Storage Card2’ then rename the folder ‘Storage Card’ to something else and re-boot).
In that discussion thread there was some mention of the Home Screen loading process being initiated prior to the SDHC card driver being loaded. In such case, if there are any references to the Storage Card locations during the Home Screen flash process (actually, I had installed few apps on the SD that displays contents on the Home Screen), then it gets into such boot loops.