Device Powers-On instead of going to bootloader mode

[Theo07]

I am a total newb and have sucessfully flashed an 8125 with the reTOUCHed rom and now looking to flash an 8525, however whenever I try to flash the device it powers-on instead of going into bootloader mode and going through the full reflash process. I have read a lot of the threads and only found one post specific to this question and not seen an answer. Any help would be much appreciated.

Thanks.