PC hardware forum: PC longevity: what usually causes PCs to malfunction?

\in all my years i've never had a desktop pc broken down on me while its turned on, but i've had 2 desktop pcs when i was younger and they all malfunctioned whenever i had turned them off and back on again, the agonizing series of beeps when the bios boot would usually indicate a failure in hardrive or mobo...even though every component was working fine the day before when i had turned it off. Most of my friends' desktop pcs broke in a similar manner to mine; they were all perfectly functional, but when the next time they are turned on, something in the mobo breaks/malfunction/fries, and so within less than 24 hours, a perfectly fine and healthy pc, dies.

i've read that heat will shorten a desktop pc's lifespan, and that a pc left turned on continuously will experience a shorter lifespan compared to pcs who are regularly turned off and cooled down, however i've learnt from a friend who works in the local library that the internet pcs there for the past 5 years have never been turned off since all 80 or so of them are secured and locked inside the desk drawer and they decided that it would take too much time to have to manually turn them on on each floor one by one. for the record mainframe/severs they are only putted on Sleep mode and its been like this since the library opened 5 years ago and they've only had 6 pcs broken down, meanwhile all my classmates and friends at the university,most with branded pcs like hp and dell all had their pcs replaced on avarge by the third year from when they purchased it, ALL of them having their pc simply malfunctioning when they turned it back on again, and as for me i've own 2 pcs in the past and they were all working one day and when i turned them off and back on again, something always goes wrong and would require hardware and parts replaced entirely, (the HD mysteriously failed, nvidia stopped working, continuous reboots, cd drive..dead! mobo? yup, dead!) but in all my experience i've never ever seen a pc Hardrive failing when its turned on, i've never seen a video card failing outright when i'm watching movie, nor motherboard frying up, nor rebooting continuously, nor anything! simply put, when my pc is turned on, everything is always ok, its when i turned it off, something will break when i turn it on again!

so i've got a couple of things i'd like to ask.

1: are desktop pcs designed to be turned on for even years and years? if there is sufficient cooling?

2: do you think sleep mode is better than shutting down the pc? and is it true that heat is harmful to desktop pcs? (i know it is for notebooks)

3: how many ppl here actually have a component, like video card, mobo, hardrive...etc on their desktop breaking down/failing on them on them while their pc is still turned on?

4: and how many ppl here have their pcs malfunctioning when they turned it back on again even though it was previously in good working order?

5: overall, do you prefer to leave your pc on or would prefer to using sleep mode than shutting down?

6: what do you think decides a pc's life expectancy?


thanks for sharing your thoughts!

~cheers