Disconected battery for 5mins now the alarm goes off when doors opened but engine still starts Toyota corolla 1998.

I would change the battery and make sure it has a good charge. Or take that battery to auto parts store and have them test the battery to make sure it is good. If it is, have them do a fast charge. If that don't work I say you might have a grounding issue

You need to reset the alarm system to get the car to start.

Same here... I have a 1998 Toyota Avalon XL. My car battery died. Replaced my car battery, but found out that when you unplug and plug the car battery with this car it engages in security mode (I have factory car alarm). This disables the engine and wont let you turn the ignition aka start the car engine until the remote (keyless entry) "UNLOCK" is applied. My remote is also lost so I cannot disable the alarm.
The only thing I can think of to do is unplug the battery again to disable everything (car alarms are annoying...) and call the dealer to pick the car up and perform the diagnosis. Most likely they will offer you another keyless (ugh... expensive) and/or you could ask to disable the factory car alarm.
I know thats not much help but it seems to be the only option from what I researched currently....

have u checked and replaced the battered in ur alarm/central locking fob ??

i would check the fuel filter, if thats good, it may be a grounding problem, my corolla was doing the same thing, making me so mad! LOL turns out the battery was just bouncing up and shorting out on the hood! any way good luck and hope this helps

somehow the car when on valet mode, go to a alarm shop , they should be able to re arm your car without to much damage to your pocket, or read your cars manual, it might inform you on how to fix the problem.

Simple thing to do is have your coils checked.. You should have spark if they are good.. If you still dont then disconnect battery at least 20 - 25 mins see if it resets ecm and alarm. May begin to work properly again..

I had the same problem, i had to remove the whole alarm system to get my car to start, when you unattatch the battery cables, the alarm notices the battery drain and sets the alarm off, i have no idea how much the dealership would charge for a new remote, but im sure its pricey, i would recommend just removing the alarm system, temporarily, until you can get a new remote. Good luck and god bless

Try your fuse panel. You must have blown the ignition fuse when replacing the starter.

Your Central locking wire is short from any one door side. Please check it properly.