Capacitors don't have to show any outward signs of failure to have either failed or be failing. In many ways electrolyte leakage, exploding tops etc are extreme examples of failure - they're by no means the 'norm'. Most of these capacitors have 1,000 hour MTBF's and maximum operating temperatures of 85 degrees, which shortens their life. If you want to know more about this subject, this site is very informative - http://www.badcaps.net/.
Please don't think that just because there's no signs of failure, that they haven't failed or aren't failing.
Look up the make and model number on google and find out what the power requirements are.
It brings them up to their usual operating temperature and can often coax them into working long enough for you to boot the machine. This is not a 'fix' it's a diagnostic method to help identify if your capacitors are failing. If they work when warmed up and won't when cold then you have your answer.