Possible IMAC HD/RAM failure-help please!

I have a mid-2007 iMac that had a hd replaced under warranty when it was about 2 1/2 yrs old. Now the same mac is crashing (meaning random terminal beach ball, which can only be fixed by powering off with the power switch) with increasing frequency, sometimes only running OK for a few min. tops. I re-formatted the HD, reinstalled Snow Leopard, and did a Time Machine restore (running Snow Leopard up to date). It ran fine for about 2 days then the problem popped up again. Apple Hardware test checks OK, and verify disk checks OK. Could this still be a failing HD, bad RAM, or what? Any suggestions on the guilty culprit? There are no sounds inside the unit except maybe normal HD sounds. Please don't let me down, I've been such an Apple fan since I switched in 2007. Thanks.

Disk Utility verify and repair only looks at and repairs any file or folder inconsistencies but does nothing to check the hardware itself. For that you need to use the S.M.A.R.T. utility for OS X which you can download from here.

From your description of the symptoms, it does appear that your hard drive may be failing.

chscag said:

Disk Utility verify and repair only looks at and repairs any file or folder inconsistencies but does nothing to check the hardware itself. For that you need to use the S.M.A.R.T. utility for OS X which you can download from here.

From your description of the symptoms, it does appear that your hard drive may be failing.

Click to expand...

I ran the SMART utility and it says all is okey-dokey. Could this still be HD failure?

If the S.M.A.R.T. utility said the drive is OK, we have to assume that it is. The program is generally right on target, of course there is always Murphy's Law in play...

The beach balling could also be caused by a runaway process or program. Open up your Activity Monitor from Applications, Utilities, and see if there's anything that's eating up the CPU. Programs, processes, etc, could be using all your memory or CPU causing the eventual crash.

This can happen after the mac has been idle for hours just after wake-up, browsing in Firefox or using Mail to check e-mail, other than normal background tasks there isn't a lot of multitasking going on.