COMPTER FREEZES/CRASHES in minutes IF TOO MUCH USE

USING: ABIT BH6 motherboard with 1.3GHz Intel Tualatin processor using
an adaptor. WD 250GB & WD 200GB harddrives connected to motherboard
with Promise Ultra 100 IDE controller card that came with the WD 200GB
Hardrive. Video Card - Ati AIW 128 PCI 16MB.

BEFO Windows 98(not SE) was loaded onto WD 8GB hardrive, attached
directly to the motherboard, no Promise Controller card needed.
Everything worked great. The larger harddrives did have to be attached
thru the Promise controller to be recognized by the older motherboard,
and they were used for storage backup only. Was a perfect setup, worked
flawlessly

NEXT: Wanted to get rid of old WD8GB harddrive, so loaded new
Windows98SE onto larger 200GB harddrive, which has to be attached to
motherboard with Promise ATA controller to be recognized.

NOW -Problem: computer freezes/crashes, blue screens, or green screens
when using any application too long (within the hr), or worse if using
many applications at once -multitasking (within minutes). If have too
many IE windows open will crash immediately. Also if trying to download
something too large (10-50MB, depending) will freeze before completion.
If downloading attachment from Outlook Express will usually crash if
attachment is 3MB or more. Sometimes less. Also crashing is never the
same. Sometimes can squeek more usage out of computer, other times
crashes quickly. Also if trying to transfer/move any large file (100MB,
sometimes only 50MB, sometimes 200MB) from one location to another in
Windows Explorer, will freeze/crash computer. Then when restarting
computer after the crash, Scandisk (i use Norton Disk Doctor) always
says some files or structures are in error and I end up having major
problems, like apps not starting, or email completely deleted, then
have to use Go-Back to recover, then start over. What a pain in the
butt. NOTE: NONE of this EVER happened "before"(see top -"BEFORE").

WORK-AROUND: The only way I'm able to get anything done is to manually
restart the computer before I "feel" it's about to freeze/crash. This
"buys" me more computer use. If I do this every 10-20minutes or so,
depending on usage, I can use the computer all day or forever without
crashes. This is EXTREMELY annoying to have to do -close all apps, save
everything, then restart, open apps, continue working, REPEAT IN
10-20MIN. PLEASE HELP.