MY VEHICLES REMOTE CONTROLS STOP WORKING. HOW CAN I FIND THE PROBLEM AND CAN I FIT A AFTERMARKET SYSTEM?

Not to worry friend, when my car go sick i avoided going to mechanic looking for DIY_Repair when I found this website https://big-manuals.com/ and this book helped me repair it within an hour, all by myself!!!
From wiring diagrams, schematic illustrations, spark plugs info, parts info, chassis number, valve time settings, step wise instructions, torque specs, error/fault codes, engine info, to every single minute parts, you get everything in there you can't imagine how detailed it is

Which vehicle is this alarm fitted to? Is it a factory fitted system or an aftermarket one? Have you checked the battery in the remote works? More information is needed to fix your problem

Try cleaning, scraping the battery contacts and then put a little petroleum jelly on the contacts and reinstall batteries. If they leaked a bunch then you may have a copper trace or a wire corroded in two.

This sounds like as you have explained the removal of the factory fitted stereo is connected to the controls/ steering column by fitting the new stereo some electrical items remain unconnected. The volume control may be in circuit.
I have experienced this before on other models when fitting non factory extras.

Is this an issue with all 2008 HHR remotes??? Highly doubtful , probably the vehicles keyless entry system . Taking the vehicle to a qualified repair shop an having the keyless entry system checked for DTC'S - diagnostic trouble code's . Do you know what a DTC is ?
The keyless entry system is a vehicle entry device. The keyless entry system is used in conjunction with the body control module (BCM) to remotely activate certain vehicle features. Keyless entry will lock/unlock the doors, or release the rear compartment lid when a corresponding button on the keyless entry transmitter is pressed. This is accomplished by the transmitter sending a radio frequency to the remote control door lock receiver (RCDLR). The RCDLR interprets the signal and activates the requested function via a serial data message to the BCM. A low transmitter or vehicle battery or radio frequency (RF) interference from aftermarket devices, such as 2-way radios, power inverters, computers, etc., may cause a system malfunction. High RF traffic areas may also cause interference that could lead to a malfunction. Keyless entry allows you to operate the following components:
• Door locks
• Liftgate lock
• Remote rear doors (Panel only)
• Vehicle locator/panic alarm
• Illuminated entry lamps
• Remote vehicle start
The keyless entry system has the following components:
• Keyless entry transmitters
• Keyless entry antenna
• 2 Way Advanced Remote Start RCDLR
• BCM

Guessing will not fix this .

Hello. Welcome to FIxYa. Please allow me to assist you. It appears that you might have a factory alarm system on this vehicle. Try cycling the key in the ignition from lock to on (not to start) 5 times. This procedure is built into the factory system if the battery in the remote goes dead, or if the remote gets lost. One note, however.This procedure will only work on the Factory system. If you have an aftermarket system fitted, this trick will not work.

this usually happens when the battery has been disconnected from the vehicle, what happens is when the battery is disconnected the locking system fitted to the car has a pass-code that only the key-fob can access, as a result of the battery being removed the pass-code for the locking system on the car resets and does not recognise the fob being used. Your best chance to get this sorted is to take it into your local garage/dealer and get the fob linked back up to the cars locking system.

What else do you expect from a boy racer sunday mechanic system,rip it out and just use a crook lock ,Nothing but trouble these aftermarket stirling mose or halfords made in china junk .The chips used are poor quality and always go wrong.Also it wouldnt stop me for more than a few minutes to steal car just cut battery earth cable from below the lift car with tow truck.easy

these vehicles had a zylux immobiliser fitted at point of entry to Australia others had after market system fitted they didnt actuall build them with these features.you need to go to a dealer to repair or program new remote, have you got a second key remote? this one might still work

As with most vehicle theft systems they have a life expectancy and the control unit may not be working correctly but try hooking the ground to a better stripped location. I usually find an area on the frame and sand off the paint then use a self tapping screw and reground it then try it if not purchase another aftermarket system and have it installed professionally most aftermarket systems are better anyways and last longer plus they come with warranty. Heres a good site to buy one at wholesale.
http://godspeedaudioheaven.wholesaleaudio.net/