hi all ,i have a problem my NC30 just lost power and i tried to start it and the battery was flat, what can cause it to happen? coz when i jump it using another battery it starts, but after switching of after a while the battery stays dead.....

Reg/rec has probably died have a look on here loads of ways to test and stuff theres a guide in the document section

If the battery is flat, there's obviously not much point in measuring it with the ignition off, but if you can get the jumped again, measure the voltage across the battery at idle and at 5000rpm. You should get approx 12.5V and 14.5V. If the figures are lower, then the battery is not being charged. If the figures are higher, then the battery is being over charged, which can damage it and lead to it not retaining any charge. If you have more than 16/17v at 5000rpm, do NOT use the bike with the current reg/rec, as if the battery isn't knackered, it soon will be, and if you buy a new one, it will be ruined in short order! If the voltages check out OK, then it's most likely that just the battery that is at fault.

As Nazz says, there are plenty of threads about on the forum to do with checking dead batteries and dodgy reg/recs, as well as improving the charging circuit, so have a quick search and let us know what the results are!