T40 slows down when switching from ac to the battery

1. Faulty RAM - try to remove, clean, re-align.

2. Remove battery, press power button for at least 30 secs. w/o AC power. Attach to AC power without

battery. power on. Hard reset

3. Faulty Processor - very risky of dismantling and aligning processor.

4. MOBO problem.

It sounds like a driver issue. Check for any updates to drivers for your laptop from the toshiba website.

if you have a restore disk, you may wish to back up any important information and use it to reinstall your operating system to factory default. Since it charges when turned off properly, it does not sound like a hardware issue.

You should replace the battery. I wish I had a better answer, but that's pretty straight forward.

You have an option here to check what the problem is....first I would like you to get a can of compressed air from an office supply store that is used for blowing the dust out of electronics. Blow the dust and dirt out of the vents on the side, bottom and rear of the laptop. I then would like you to run the laptop on the AC adapter only to see if the ac adapter is the problem. So take the battery out and run the laptop just on the AC adapter. If it shuts down, put the battery in and remove the AC adapter....if the machine continues to operate, the problem is AC adapter. It is most likely failing after a period of time causing an unstable power source and sgutting the laptop down....or if it fails on just battery too, then I would take off the panel access door to the processor and heatsink, remove the screws to the heatsink and carefully remove it and check that there is a layer of "thermal grease" on the two processor chips. If not, get some thermal grease and apply a very small amount and spread it evenly on the chip surface. Replace the heatsink and try to power it up.

if you think your adapter really works fine then you have a  motherboard issue.

Have you disabled your battery
is your battery showing
check control panel\power options
does your battery show as 100 % charged
then you can also check device manager for battery
Let me know

Bad battery, needs to be replaced.

There are several possibilities. Let's start with the easiest two. First the battery, take it out and try starting up only with the power supply. Then the memory chips. If a memory chip fails it can cause a no start in IBM's. Take the memory out and try it. Then try it, putting them in one at a time. If these don't work, then I'm afraid your problem lies within. Namingly the power management chip on the motherboard. The pm chip controls the power input, and allows such functions as switching between battery and AC, and battery charging. The pm chip can go without warning, and just because it lights and shows charging doesn't mean this chip hasn't malfunctioned. I've had several IBM's come through my shop that have experienced the same problem you're describing. I've also had them with problems like; it will only power with the battery, won't charge the battery, will charge battery and only run with battery shuts down while charging, only power under AC, etc... all pm chip related issues. Unfortunately, the only solution is motherboard replacement.

Simply plug the ac adapter into the wall, the laptop will charge the battery itself.

Keep in mind this... in general, a laptop runs at full speed when it is plugged into the wall. When most laptops are running on battery, things are running more at 50% capacity to save on power, this giving you more battery life. A dimmer lcd and slowing the processor down when not needed are common traits.

You can use the FN key (function key) and the corresponding dim control on the keyboard to adjust the brightnedd of the backlight. It should be marked on your keyboard in a different color, like blue or maybe green (not familiar with that models keyboard).

 

It would have done, because when running on battery the laptop goes into power saving mode and the brightness and processor would be slowed down. If you go into your power settings of the laptop, which will probably be in the taskbar as a battery icon, right click on it and you should be able to change the brightness settings or use the 'Fn' and the Star shaped icons normally on the right and left keys or within the power options in control panel.