Water Leak and Car Wont Stay Running???

[northern1999]

Had a water leak that would get the passenger side carpet moist after a good rain. Had a couple of days where it rained alot, after that found water sitting in the passenger side. Drove fine for a couple of hours, after that care would not stay running for longer than about 3-4 seconds. Took all fuses out and checked them, then car started fine. Next morning all gages were dead, but car ran fine. Took to mechanic and got water leak fixed, and they also replaced main computer. Went to pick it up and same problem. None of the gages worked again and car wont stay running fro longer than 3-4 seconds. It is a 99' Alero with a 3.4L. Thanks.