Many kernel panics, possible dead logic board?

Question

I hope someone can help my diagnose my recently quirky iMac G4 1 ghz 17 in flat panel. I currently have a 250 G Seagate hard drive, 1 G memory. It's running Tiger 10.4.11...or attempting to run it.
This computer ran beautifully until several weeks ago when I foolishly attempted to upgrade to Leopard. Only about a third of Leopard got installed when the system froze and crashed. I managed to access the hard drive and did a complete wipe and install of good old Tiger, upgraded to 10.4.10 which ran without a glitch in the past.
However, even after this clean reinstall I continued to get freezes and kernel panics. I repaired all permissions carefully after each upgrade and I ran Disk Utility with no problems detected and no repairs needing to be done. I tried to run Disk Warrior to double check but continued to have system freezes and kernel panics while running Disk Warrior!! The panics were/are intermittent. The computer behaves fine until I've used it for a few hours, then crashes, usually while I am in Safari or iTunes, but occasionally I will get a panic at start up.
I have replaced the hard drive with a brand new one as it was still under warranty. I tested the memory and determined by process of elimination that the stick of RAM on the logic board was not functioning. I replaced that.
So, I have a new hard drive and functional memory and tried a Tiger fresh reinstall yet again today. The system continues to crash episodically...used the computer for a few hours this am before I got a kernel panic. This afternoon it resuscitated itself enough to let me put upgrade 10.4.5 on it and crashed in the middle of the upgrade! Bear in mind the machine's run all these upgrades and functioned fine in the past.
I think I obviously have a hardware problem and since I've recently replaced the hard drive and both memory modules as well as done a fresh reinstall of the OS version this iMac used to run perfectly, I'm thinking I have a logic board issue.
Any opinions or suggestions on how I might get these issues worked out would be very much appreciated!

Answer 1

Thanks for responding. Yes, I've already followed all those suggestions to the letter. Unfortunately I do not have the original Apple Hardware Test disc that came with this computer. I have oredered a copy of Tech Tool Pro and plan to run it but it has yet to arrive.
I let the computer rest overnight and it booted right up and so far no freezes or panics, I've been using it about a half-hour.
Of note, in the kernel panic log folder it says,
Unresolved kernel trap(cpu 0): 0x300 - Data access DAR=0x0000000017FCBA10 PC=0x0000000000081F1C
Latest crash info for cpu 0:
Exception state (sv=0x2E9CC780)
PC=0x00081F1C; MSR=0x00009030; DAR=0x17FCBA10; DSISR=0x42000000; LR=0x0008223C; R1=0x17FC3A60; XCP=0x0000000C (0x300 - Data access)
Backtrace:
0x0008223C 0x00062D04 0x000A81F8 0x000ABD00
Proceeding back via exception chain:
Exception state (sv=0x2E9CC780)
previously dumped as "Latest" state. skipping...
Exception state (sv=0x2E9CB000)
PC=0x00013110; MSR=0x00009030; DAR=0x006D55FC; DSISR=0x40000000; LR=0x0001227C; R1=0x17FC3DA0; XCP=0x0000000C (0x300 - Data access)
Backtrace:
0x00000002 0x0001227C 0x00022864 0x000AC02C 0x1E010000
Exception state (sv=0x2EA7A780)
PC=0x9000B208; MSR=0x0200D030; DAR=0x901A640C; DSISR=0x40000000; LR=0x9000B15C; R1=0xBFFFF100; XCP=0x00000030 (0xC00 - System call)
Kernel version:
Darwin Kernel Version 8.4.0: Tue Jan 3 18:22:10 PST 2006; root:xnu-792.6.56.obj~1/RELEASE_PPC
panic(cpu 0 caller 0xFFFF0003): 0x300 - Data access
Latest stack backtrace for cpu 0:
Backtrace:
0x00095718 0x00095C30 0x0002683C 0x000A8384 0x000ABD00
Proceeding back via exception chain:
Exception state (sv=0x2E9CC780)
PC=0x00081F1C; MSR=0x00009030; DAR=0x17FCBA10; DSISR=0x42000000; LR=0x0008223C; R1=0x17FC3A60; XCP=0x0000000C (0x300 - Data access)
Backtrace:
0x0008223C 0x00062D04 0x000A81F8 0x000ABD00
Exception state (sv=0x2E9CB000)
PC=0x00013110; MSR=0x00009030; DAR=0x006D55FC; DSISR=0x40000000; LR=0x0001227C; R1=0x17FC3DA0; XCP=0x0000000C (0x300 - Data access)
Backtrace:
0x00000002 0x0001227C 0x00022864 0x000AC02C 0x1E010000
Exception state (sv=0x2EA7A780)
PC=0x9000B208; MSR=0x0200D030; DAR=0x901A640C; DSISR=0x40000000; LR=0x9000B15C; R1=0xBFFFF100; XCP=0x00000030 (0xC00 - System call)
Kernel version:
Darwin Kernel Version 8.4.0: Tue Jan 3 18:22:10 PST 2006; root:xnu-792.6.56.obj~1/RELEASE_PPC
I hope this might help. Thanks again.