Check if your platform stores console outputs and check when this is the case if something explains the reset.
Check also on hardware log if this one exists.
I checked the ILO logs but there is nothing there.
I was thinking, if its good to generate crash dump in such instances.
I know we used to send break signal to hung solaris and then run sync command at OK prompt.
then it generates a panic sting and crash dump.
can we generate crash dump in case of solaris on HP system to analyse the reason behind hang.
If you have the crash dump file you can analyze it with mdb:
You can certainly generate it but I don't know how we can do it with HP platforms.
Please read the following document for more details : Solaris[TM] Operating System: How to force a kernel core dump on an x86 or x64 system (Doc ID 1003085.1)