Just been to in-laws to sort out pc. When on the windows login the cursor/pointer jumps about all over the place, so have left clicked and entered password and when windows has finished booting it works fine. I have tried usb optical/wireless and ps/2 mice and it has the same effect

Assuming the PC is free of malware (see Cleaning Out Malware if you do already have a complete arsenal), there are three options - try and test in order.

1. Go to Control Panel > Mouse and uncheck Enhance Pointer Precision.

2. From Control Panel > Add and Remove Software, uninstall current mouse drivers (remove from Device Manager if Control Panel option is not present), shut down Windows, power off PC, unplug PC (or turn off master power switch on back of PSU, if so equipped) for 10 - 15 seconds. Power up and follow prompts to install new drivers.

3. Follow steps in MSKB Article 321122, The Microsoft mouse pointer moves erratically or does not respond when you use a Microsoft pointing device.