Battery won't charge in either laptop

My daughter's laptop (Compaq Presario C300) started having problems about a week ago. It wouldn't charge the battery. She got a new battery and it worked fine for an hour and then shut off. The battery wasn't charging.

My son has the same laptop. He used her charger yesterday and it was working better than his aftermarket one so he continued using it, then his cat laid on the cord and it got jerked out of his laptop. After that his laptop stopped charging the battery too.

We tried his battery in her laptop and her laptop worked fine with the charged battery. It still wouldn't charge it though. We tried her battery (both the old one and the new one she bought)in his laptop and it wouldn't charge (the light wouldn't even stay solid). After that his computer started having the same symptoms that hers did (flashing charging light.) We took the power adapters to have them checked and they said they are fine. We bought another battery and my son's laptop works fine with it but it won't charge that battery either. It does show a solid light in my son's laptop as if it's charging but it isn't. I originally thought hers might be the cord or the jack but now his has the exact same problem. Could the cord have messed it up? Or could it be coincidence and they both have problems with the jack?

Is there anything we can do or do they both have to give up and get new laptops? Thanks for any help you can give.

 

My son just left with his laptop so I can't try anything on his. After buying the new battery and putting it in his, it drained the battery but continued running with the AC cord plugged in. The battery won't charge.

I tried cleaning the contacts in my daughter's laptop. When I put the battery back in and plugged it into the adapter, it showed all three lights on the front and the fan tried to come on before it quit. We had shut the computer down the last time it was on so I don't know why it was acting as if it was turned on. Right now it's back to having the charging light flashing strangely. It won't turn on and it won't charge. Should I keep trying to clean the contacts more?

 

I left the laptop plugged in all night. The charge light flashed dimly. The whole bottom of the laptop was still cool to the touch this morning and it still won't even try to turn on. We did mention this to the place where we had the chargers checked but I wasn't too impressed there. He tried to tell me that the battery from my daughter's computer could infect my son's computer with something and that might be why it won't work either. He used one of their chargers and plugged it into my daughter's laptop and it did the funny blinking. He said there was something more wrong with it than just the battery and of course his diagnosis was the motherboard. I still think it might be the jack.

When I say charger, I guess I should say power adapter. It's just the cord that plugs into the wall. I did actually find a stand alone charger online but it's almost $70. I'm attaching a picture of the charger we have.

My son turned off his laptop when he left here and when he got to his house he plugged it in and turned it back on. He said it lasted 10 minutes and then quit working.

On both laptops there is one screw that will not come out of the back to take it off and check the power jack. I don't know what to do to get it off. Then we could try replacing that or at least checking to see if the connection looks good. Any hints on getting out those screws?

I just found a picture of the power jack assembly. It would be easy to replace but it's also over $40 and I'm not sure that's what is wrong. Is there a way to check it before I try ordering something like that? We still can't replace it without getting the back off either!

Thanks for all your help so far!