Computers are complex, so when something goes wrong it can be difficult to figure out what the cause is so that the issues can be resolved. Knowing the correct things to ask the client can assist a technician in the troubleshooting process.
Some useful questions to ask;
When did this problem start occurring?
Has this problem occurred before?
Has anything changed recently with your computer?
Has new software been installed?
Has new hardware been installed?
Which application were you using when this problem occurred?
Does this problem happen every time?
Some useful things to try;
Replicate the problem.
Test with a known good system.
Check all cables.
Disconnect unnecessary hardware.