27" early 2013 iMac Overheating?

27" iMac, 3.2 GHz core i5 24 GB DDR3 3TB Turbo, GeForce GTX 680MX 2048 MB, OS 10.9.2 (13C64).
iMac began flickering, control degraded, launchpad out of control, Time Machine not accessible, display random weirdness.
Several restarts extremely slow shutdown and very slow strange restart sequence, opened with same if not worse situation. Random windows opening. Desktop icons flickering.
Panic!. Shut down, had breakfast.
Restarted after about 30 minutes.
Everything normal. No problems. Norton antivirus running now.
History - computer on 24/7, frequent overnight iTunes music operation.
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New plan - shut down at night.
Anyone else have this type of problem?

Update: Norton Antivirus complete, no viruses found.

 

Heating?

I'm guessing and not very confident about it. It's been running 24/7 with 16 GB added 3rd party Kingston RAM except for local power outages with no prior problems. Powered on APC Back-UPS RS1300 but is shut down manually on power outages. No power interruptions around day of incident. Mine also quite cool.

Decided to resume 24/7 after rethinking history.

45 years using several dozen different hardware systems including about 10 different Apple configurations says 24/7 usually best plan.

Probably random software glitch while switching rapidly between several Microsoft Office windows. Most of the incidents I've experienced on Macs have been with Office use, but never had my Mac go completely Ape like this incident before. NOTHING worked until I left it totally off for about 30 minutes.

Hence suspected heating possibility. Remembered several forum mentions of possible heating problems shortly after this machine first hit the market. Mine is a very early one.

Normally never buy new anything in first six months, but my old G5 was dying/gasping and have to have a working computer.