Flexible water supply tubes have been known to fail long before the water heater itself is ready to retire. If there is insulation, be sure to remove it to see if it is wet underneath. To replace the flex lines turn off the water supply and the water heater itself. If you feel like the job is too big for you, call a licensed plumber.
There is also the option of calling a professional for an inspection and estimate. Knowing exactly what the problem is and how much it will cost to fix it is usually worth the cost of the service call.
You may also want to look at our Plumbing Page.