Grasping at straws- It could be anything-
Its too bad you weren't informed of this when it started. Maybe it coulda been nipped in the bud if it's a software corruption or conflict prob. OK here it goes. Random thoughts.
Are they Hangs ( frozen screen, cursor moves),
freezes (frozen screen, frozen cursor) or Crashes with an error message?
You've zapped your PRAM with tech tool?
Have you tried Conflict Catcher for extension conflicts? A full 7 day demo is available here: (it's good to keep in your bag of tricks.
(It also really helps when reinstalling/reformatting by helping restore the system folder.)
Could be SCSI. If you can, try to reproduce crashes with your Ext. SCSI chain disconnected.
Try Dragging application prefs out of the system folder> prefs file and putting them in a folder outside of your system folder for safekeeping.
The prefs will be rebuilt when you restart. You'll have to reset some app prefs, but it's a standard trouble shoot tool.
Try starting up with only base extensions enabled the see if the HD shows up on a soft resrart.
Do a clean OS install.
Save everything and reformat, reinstall the OS, get the latest driver set up 1.7.3 from Apple, reinstall apps 1 by 1 and test after each installation.
Nothing has worked?
Open 'er up. It's a pain in the butt with that machine. Not hard, but a pain.
Find a logic board diagram here:
MacGurus is a GREAT site.
Here is a good guide for removing the logic board (which you'll have to do to get at memory etc. It's a 1 min PDF dowload. Great pictures.
Go here to get the Apple Service manual for that machine. It's a 20 min. PDF download at 56K, but well worth the wait.
Scroll down the left side to powermac 9500.
The G4 wants good memory. No cheap housebrand stuff.
All of your memory should be EDO, 60 ns, 2K refresh, have chips on the module from the same manufacturer. There are no bargains when buying memory, esp. with a g4 upgrade. There is a lot of bad memory being sold on the net. Stuff that is OK for surfing and writing Aunt Tillie may not be good enough for your memory intensive use.
Quite often the cheap stuff is memory that doesn't meet manufacturer specs and is sold to a reseller for a deep discount.
Wait! You've got a NewerTech card! Memory for a Newer brand card has to be buffered AND dampered. Look on the controller chip for the number 162244 (on each stick of RAM). If some of it (probably at least the original RAM) has a number like 16224 or 16244 (with only one set of doubled numbers I don't remember which off the top of my head), that VERY well could be the problem.
Pull the non 162244 modules, run it and see what happens.
As long as you're in there, change the battery. It can cause some problems recognizing the startup disk (it doesn't sound like it in your case) but it's only got about a 3-5 yr projected life and costs $10.
It will cause some wierd problems when it goes.
Post back if and when you solve your problems so we can learn,
or if you need/want clarification.
[This message has been edited by GLT (edited 03-24-2001).]