I found this on another forum it'll clear the EEPROM so give it a go.
MP750 / MP780 waste ink counter reset instructions..
1. Service menu: Menu -> Scan -> Copy -> Scan (one at a time in sequence)
2. Select "TEST MODE"
3. Select " ETC.."
4. Select " EEPROM CLEAR"
5. Select " INK COUNT"
6. Press the [OK] button.
7. Press the [Stop/Reset] button (returns you to the TEST MOD sub-menu))
8. press the [ON/OFF] button (which resets the printer)
TIP: Don't rush the printer as it can often take considerable time to
respond to your commands. Frantic button pressing will just push the
printer into snail mode (ie: slow as heck!).
Hope that helps... :)
try that, i stole it off