Learn how to diagnose the symptom when computer system randomly crashes/reboots for no reason.
Check for the viruses first. Some viruses (especially memory resident viruses) can cause the PC/Laptop to crash or reboot unexpectedly. So run an anti-virus program to check for viruses.
Check the power supply cables and verify that they are correctly attached and securely to the motherboard.
Use a voltmeter to verify that each output from the power supply is correct, as outlined in the below table (Table-1). If any output is low (especially the +5-V output), replace the power supply.
With all power-off, check to see that the CPU is cool, that the heatsink/fan assembly is fitted on correctly, and that the CPU itself is inserted accurately and entirely into its socket. If the CPU overheats, it will stall; taking the entire system with it.
If the CPU is seated in a Zero Insertion Force (ZIF) socket, make sure that the socket's tension lever is closed and locked into place. In most cases, this is the reason for the system to randomly crashes/reboots.
Also, check that all SIMMs are correctly seated in their holders and locked into place. You might try removing each SIMM, cleaning the contacts, and re-installing the SIMMs.
Check and make sure that all expansion boards are correctly seated. Any boards that are not secured properly or that are inserted unevenly can short bus signals and cause spurious reboots.
If you have recently installed new expansion hardware, make sure that there are no hardware conflicts between interrupts, DMA channels, or I/O addresses.
Inspect the motherboard at every metal standoff and see that no metal traces are being shorted against a standoff or screw. You might want to free the motherboard and see if the crashes or reboots go away.
If so, use non-conductive spacers to insulate the motherboard from each metal standoff. If the system continues to crash or reboot, replace the motherboard.
Table-1: PINOUTS of ATX and Baby AT Power Connector
ATX Power Connector
| COLOR | VOLTAGE | PIN |
|---|---|---|
| Orange | +3.3 Vdc | 1 |
| Orange | +3.3 Vdc | 2 |
| Black | GND | 3 |
| Red | +5 Vdc | 4 |
| Black | GND | 5 |
| Red | +5 Vdc | 6 |
| Black | GND | 7 |
| Gray | PwrOK | 8 |
| Purple | +5V standby | 9 |
| Yellow | +12 Vdc | 10 |
| Orange(22AWG) | +3.3 Vdc | 11 |
| Brown (22AWG) | 3.3 V sense | 11 |
| Blue | -12 Vdc | 12 |
| Black | GND | 13 |
| Green | PS-ON | 14 |
| Black | GND | 15 |
| Black | GND | 16 |
| Black | GND | 17 |
| White | -5 Vdc | 18 |
| Red | +5 Vdc | 19 |
| Red | +5 Vdc | 20 |
Baby AT Power Connectors
| COLOR | VOLTAGE | PIN |
|---|---|---|
| Orange | PwrOK | 1 (P8) |
| Red | +5 Vdc | 2 (P8) |
| Yellow | +12 dc | 3 (P8) |
| Blue | -12 Vdc | 4 (P8) |
| Black | GND | 5 (P8) |
| Black | GND | 6 (P8) |
| Black | GND | 1 (P9) |
| Black | GND | 2 (P9) |
| White | -5 Vdc | 3 (P9) |
| Red | +5 Vdc | 4 (P9) |
| Red | +5 Vdc | 5 (P9) |
| Red | +5 Vdc | 6 (P9) |
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