Gus,
Don't know if you've seen this extract I found at logitech's support page:
page=support/products/document&CRID=320&contentid=5659&conte
ntid2=4983&showalldocuments=0&countryid=18&languageid=1
Maybe it might help?
Marc
Q: My cursor doesn't move or jerks around the screen; what's wrong?
A: It is likely the mouse/keyboard and receiver may need to be re-synchronized. If you are using our current cordless products, just press the "Connect" button on the receiver then press the connect button on the bottom of the mouse/keyboard. If you are using a Cordless desktop system, you must do this procedure for both the mouse and the keyboard. If you are using any of our older cordless products, then please refer to document Customer Support Document #4549, "Synchronization Procedures for all Logitech Cordless Mice."
Also, any electrical device such as the computer monitor, Zip drives, speakers, etc., can cause interference with Logitech cordless products. Most likely, this will effect tracking of pointing devices or the range. Also, using Logitech cordless devices on a metal desk or a desk with a metal frame can cause problems with pointing device behavior and range. To resolve these types of issues, try moving the receiver at least 8 inches away from other electrical devices. Interference issues can also be resolved by moving the mouse closer to the receiver. You may also want to experiment with different locations and positions for the receiver, including moving the receiver to an upright/vertical position or rotated to a different angle. Another alternate solution is to elevate the receiver by placing it on a CD-ROM case or other item.
You may also notice erratic cursor behavior if you are using an extension cable, a switch box, or a port replicator. Logitech does not support using our mice, trackballs and/or keyboards with these devices. If you are using a switch box, an extension cable, or a port replicator, please remove it and try connecting the pointing device directly to the system