[X-Newbies] G3 and upgrade problems?

[Gen Hadlow Mac Impact Dbn]

Machine is a blue and white G3 300mhz with 256mb ram.

Have upgraded to a 40gb hard drive and put in a Sony CD-Writer.
Installed system 9.2.2 and installed Panther up to 10.3.3
After installing 10.3.5 the machine has a serious kernel panic on start up.

Have had to start again - but only upgrading to 10.3.3

There does not seem to be any outstanding firmware updates required that I
can tell - took it to a friend who has ADSL and hooked it up on the network
to check for software updates on both 9.2.2 and 10.3 there was no firm ware
upgrades besides some itunes & iPod updates.

When I check on the firmware of the machine its Apple PowerMac 1,11.1f4 boot
Rom built on 04/09/00 @ 13.57.32 Open Firmware 3.1.1

I have also swopped out the ram but that made no difference to the problems.

Is there any other issues that I should look into to fix this problem?

Regards
Gen