Mouse pointer is jerking and pausing when external monitor is connected

When I have my external monitor connected (24" Acer), the mouse seems to hack.
When it's only the small 13.3" of the macbook, there's no problem at all.
I tried to only use the external display with the "finger-method".
This means that you close the macbook until the space between macbook and screen is as thick as a finger. Then it will turn to sleep.
If you then press a button, it will come back from sleeping and only use the external display (until you press "detect displays" in de Display Preferences).

Still, with using only the big screen, the mouse keeps hacking.
When I say hacking, you must think of moving the mouse, but sometimes it stops moving (just a fraction of a second) and pop up on another spot on the screen.
As mentioned it doesn't happen when there's no screen attached.

The resolution of my screen is 1900*1200, but the same problem occurs when running a lower resolution.
Please help
Thanks!

I don't where you're coming up with the term "hacking" as it certainly does not describe mouse actions? Are you referring to the mouse jumping or moving erratically across the screen?

What exactly are you trying to do? It appears from the post you're attempting to operate your MacBook in clam shell mode - which means keeping the lid closed or near closed while using an external keyboard, mouse, and display.

In any event, have you tried to adjust the mouse tracking speed in System Preferences, Keyboard and Mouse? If adjustments don't cure whatever problem you're experiencing, your mouse may be dirty or defective.

Regards.

Hi! Thanks for answering so quick

I'll try to explain it different:

I think, after what you said, that my whole mac hacks for a fraction of a second. But only when the external display is connected.
The only way I noticed was because my mouse kept stopping and then moved again.
I just started an online stopwatch, and that also hacked sometimes and then went on a fraction of a second later.
Could a re-install work?

Operating my macbook in clamshell-mode was a way to test if the videocard could not run both screens smoothly, but the problem also shows up with only the external display on.

Another thing: When running Windows XP there doesn't seem to be any problem at all..

I'm a mac-noob First mac ever.

Sounds like the mouse tracking needs to be adjusted on the OS X side. What's probably happening is that with the external monitor attached, the display resolution is switched to the native resolution of the external. That will change the way the mouse moves. Mouse sensitivity seems to be more difficult to adjust from the OS X side than the Windows side.

What kind of mouse are you using? I switched from the Apple mouse (Mighty Mouse) to an inexpensive optical Logitech that I bought at Wal-Mart. It tracks and works much better than the Mighty Mouse.

You certainly don't need to reinstall the OS. That's the Windows way.

Regards.

I think what he means by Hacking is the pointer is jerking and pausing and resuming jumping suddenly after it resumes moving to where he moved it.

Not sure what the issue is but only time I have had that issue on OSX is when the CPU was being pushed by some process 100% so things were getting choppy.

What dtravis7 is implying is exactly right!
English is not my native language, so I've some difficulty explaining
I have the same problem when the mouse is not plugged in (a cheap Logitech one btw). When I use the trackpad the problem is also there.
I have the unibody macbook btw.

I checked iStatpro and that shows the next percentages with CPU-usage:
User: around 10%
System: around 25%

Oh, and there's 550 inactive memory. Could it be that?

Started the timemachine yesterday since it had been a while.
Just IF I was going to reinstall.
Now everything works perfectly fine.
Everyone still thanks for your effort

P.S. Might be working in a mac-shop soon, so I'll be more helpfull to other people too

Well, seems I was happy too early.
It still doesn't work properly.
Tried some other things which could stop for a fraction of a second (and which I could notice).
The same is for movies on the internet, movies from my harddisk, movies from a dvd, games etc.
It looks like my whole mac just hacks for a split-second and then decides to go on again. With hacking I mean it hangs/stands still/dies/stops doing anything.
As noted it happens with everything, as long as the external screen is connected (res. 1900*1200, but on lower resolutions it does it too).
Any help is really appreciated!
If no-one was able to help me tomorrow, i'll just reinstall and hope that works.
Thanks!!
Regards

I have the same problem on a new imac 27... i try with magic mouse and with a mighty mouse usb: nothing change. I made a bug report on apple site, i hope they fix this problem... it's almost impossible work with an ext monitor... sigh...
bye
patrizio

But the problem vanished if i change my esternal monitor. If i use a sony 1600x1200 the mouse hacking if i use a samsung 191t in pivot mode (or normal) no problem...

clamshell works great but magic mouse fail!

This is a problem I face as well. I have a MacBook Pro 13.3 ". Clamshell mode works great, in my case I also have a bluetooth keyboard and magic mouse (just like the kit used in iMac) however, the problem with the magic mouse is sure to fail! Sometimes it just disconnect suddenly. What is weird the most, is that If I keep the screen open a finger, it works beautifully, but whenever I close the screen completely, it happens! I don´t know what do. Does anyone have had this problem? Does anyone have solved this?

same problem

When I connect my brand new mac book pro to a brand new LG external monitor, my mouse also pauses and jerks. I'm using the new wireless Apple mouse. This is very frustrating and annoying. It gives me headaches.