Van won't start; only turns over after installing new computer.

Don't know what happened but, tried it this morning and it fired up? Hope it's not an intermittent problem. Checked the codes after running it for a while and the normal ones came up: code 12 for the battery being disconnected, code 37 which is a bogus one, due to an afterthought in the transmission by Chrysler and code 55 which is the end of all codes. Thanks for your help.