Are you still using the standard CD32 PSU? I'm not sure if a lack of power could be causing it. I'd recommend not using a Hard Drive at all in the SX-1, and going for an IDE-CF adapter and a 4GB Compact Flash card. It'll boot faster than the HDD, and it won't need any extra power.
Alternatively, you could try an ATX PC PSU and use an adapter to power it. You can get the adapters here
http://www.amigamaniac.com/atx_to_amiga.htmlIt's highly recommended that anyone with an SX-1 and a HDD use a better PSU than the Commodore one.
