What you are giving for information is equivalent to saying "my automobile won't start". Well there are about 300 reasons that your automobile won't start.
Therefore we need much more from you:
1. How much metal detecting experience do you have?
2. How much experience with a VLF type of detector?
3. What is the type of target are you trying to find?
4. Where are you detecting? How much trash? Iron & foil?
5. What are the ground conditions like? High minerals? Saltwater beach?
6. Does it consistently happen in the same geographic location? What about other locations?
7. Any sources of interference on you; cell phone, pager, PDA, two way radio?
8. Any possible sources of interference in the location you are detecting, radio towers, cell towers, etc?
9. Are there other metal detectors operating nearby?
10. Does the same happen with other coils you may have?
11. What are all of your settings, have you noise canceled, have you properly ground balanced, sensitivity setting etc etc.
The above information is just the starting point to get useful help from the forum members, and they will gladly help as they always have, when given enough information.
HH
BarnacleBill