Is there any data on this usb 4gb drive if so you might try opening and deleting the files separately
insert your pen drive
click start click on my computer you should see your pen drive
right click then select format
another way is to control panel administrive tools,computer management disk management right click on your drive select format
or you could try some of these
click start control panel administrive tools,computer management ,disk management right click on your drive select properties click tools you should see click check now click start two boxes automatically fix files and scan for and attempt recovery of bad sectors place then a tick in both boxes then select check now,start
if this does not fix the problem you might try
click start control panel administrive tools ,computer management ,device manager scroll down universal serial bus controllers you should see a yellow question mark?
right click to reinstall drivers or
if you can see your usb but its not working
ports(com&lpt)right click update driver or
scroll to disk drives if you can see your drive + to expand right click you should see options to update driver,disable,uninstall scan for hardware changes. or
select properties you should see options in the general tab to troubleshoot,policies,volumes,driver and details under the driver tab you will have the options to check the driver details,update driver,rollback driver or uninstall
hope this helps