I turn on the the laptop, power comes on but computer does not start. I though that battery is bad or not charging, Change battery with ither Thinkpad t42 but still power light comes on but it does not start. Any help?

You can start by checking that charge cord has power out to lap top with a multi meater or voltage indicator if there is then it is ither the l.e.d. is burned out or if there is power all the way to the baterey then mostlikely a battery has built up a "memory" when we recharge a battery that has not been discharged properly it builds a "memory" and will only take a partial charge

Either your battery or the power cord has an issue. Does the battery ever fully charge and make the charging light disappear or turn green? If not the battery could be bad.

Try running the computer off the battery by removing the power cord. if the battery starts losing charging strength real quick then your battery is bad. I've see bad batteries that say they are 100% charged but as soon as you remove the power cord it gets down to 5% i a matter of minutes.

Try running the computer on just the power cord. If it stays on and lets you operate without any problem then the power cord is good. A good power cord will not charge a bad battery.

If the laptop does not let you stay on long with the power cord, then either the power cord is bad or the DC Power Jack where the power cord plugs into the laptop is bad. If either of them is bad they will not charge a good battery.

Check your DC Power Jack which is where the power cord plugs into the computer is bad. Take an ink pen and push the tip inside the jack and see if the little pin wiggles, if so the jack is bad. You'll have to take the laptop apart to fix it. Most times it is soldered onto the motherboard, so you will have to desolder the old and solder a new one.

What do you mean the new batter is not working? Does the computer turn on with the Power Cord? If not, the power cord is bad and cannot charge the battery. I have seen times when new batteries are defective. The new battery does not come charged so you have to plug in the power cord and let it charge overnight.

That is a signal that your battery is almost dead or drained. If you have the power cord plugged in and the battery is not charging at all, that means the battery is dead and you need to purchase another one.

In windows xp you should be able to click Start/Control Panel/Power Options. When the power options window opens click the Power Meter tab. It will tell you if your battery is charging.

Now to isolate if it's really the battery that's dead or if it's the Power Cord that's bad. You might really be operating on battery power even though you have the power cord plugged in.
1) Turn the laptop off and remove the battery. Turn it back on with only the power cord plugged in. If it comes and and boots up ok, then your power cord is ok.
2) Turn the laptop off and this time put the battery in, but leave the power cord off. Now hit the power button and see if it boots up. If it does that means you might have a little power still left in the battery, but since it was not charging when the power cord was plugged in, the battery is bad because you verified in step one that the power cord is good.

You have a bad or loose DC connector on the system board:

Symptoms of a broken power jack
1. If you wiggle the power cord or the AC Adapter connector on the back of the laptop, the power LED and battery charge LED start to flicker.
2. Battery will not charge in the laptop.
3. Laptop runs fine off a charged battery.
4. With the AC Adapter connected the laptop appears to be dead.
No power LED or battery charge LED activity.
5. Laptop randomly powers off without any warning.

If your laptop is out of warranty, then you can fix the problem by resoldering DC-IN jack on the system board. If it

I’m happy to assist further over the phone at https://www.6ya.com/expert/joe_8b8c2cd6ce148309

Try to perfrom power drain. You must first turn off the computer. Take out the battery and unplug the power adapter. Press and hold the power button for 30 secs. Put the batter back in, plug in the power adapter and power ip the computer then observe.

Let me know if same issue will happen.

If you need further help, reach me via phone at https://www.6ya.com/expert/elixirjose_00375ea24bd8141b

The batterycould be old.
lithium batteries does not go dead when old
You simply cannot get the energy it stores.
That isthe draw back with them.
Other wise they would probably last forever.

Will the old battery (that you are replacing) charge up at all? If the old battery charges but the new battery will not, then it's likely a bad replacement battery.

To rule out the possibility of a corrupted battery meter inside of windows, you may wish to leave the laptop on battery power only, until it dies. A 5% charge will usually only grant you about 20 minutes of laptop life maximum. Since you left it charging all night, you should get a few hours of life before it dies. If you get a few hours of life, the battery meter software is corrupted.

Most likely though, the replacement battery is bad.

The inverter inside the lcd panel is most likely your problem. Try removing the whole lcd screen from the laptop if you are capable and run it with the external screen to confirm. leave the lcd switch off (this lcd switch above the power button turns the lcd inverter on and off)

allow battery to complete charge (green lite)
Or change battery if chrge not completing.
(check your AC charger)