Hi Andrea
The SPI is normally not populated on an sabresd board if this
is what you referring to. You can build a u-boot image and
boot your board from SD. If you have a JTAG tool, try to
halt after reset and check if you can read part of ram to make
sure your board is alive. I am not sure which red light you
are referring to. Perhaps you can check in its user guide to
see what a red led is indicating.
In either way, if your board is still alive, build an u-boot image
for your board and place it to an sd card as explained in
several places in this forum. Then you will be able to boot
your u-boot and you can continue loading a Linux image.
Hope this helps.
Sinan Akman