This happened to me with a w700... Flashing MAIN and FS with XS++. The phone works while not customized. When I customize it with XS++ it was dead. After flashing again MAIN ans FS the phone works... So I used FAR manager K750 CID49 boot scripts and k750 MAIN SSW firmware (5 flashblocks) to open the W700 with far manager and put the custom files... Then the phone worked...
Anyway i didn't succeeded to finalize it using XS++ :(