If simple remedies, such as grading surface soil or patching interior walls, fail to cure a wet basement, you must block moisture outside the basement wall. No amount of interior patching will stop penetration cause by the power of substantial subsurface water pressure, nor will it plug leaks through cracks opened when the roots of a tree penetrate.
To waterproof your basement wall from the outside, you must excavate at least part of the foundation of the house, a heavy job you may want to have done. You also may prefer hiring a professional if basement walls must be resurfaced with concrete. But the rest of the job is fairly simple to do yourself.
Some cracks are shallow enough to block by simply excavating the upper part of the basement wall to a depth of about 2 feet and waterproofing with asphalt foundation coating and polyethylene plastic sheeting. If the leak is lower down, there is no alternative to excavating the entire basement wall down to the footing.
Once the digging is done, you should waterproof the wall with concrete and also lay drain tiles, which collect subsurface water and carry it away from the house. The tiles made like storm sewer piping, but generally perform rated are available in several materials in various lengths with connectors and elbow fittings. Tiles that are asphalt impregnated and rigid plastic types are the easiest to use.