but if my Internet goes down and I have to reboot my modem will that cause me to not solve any block if any luck..or does it continues off the current share..
There's no "continue off the current share", there is no "current share". Your miner works on the current block until it gets notification from the pool to switch to a new block. You must be online to work on solving a block, if you go offline you will stop mining, but once reconnected your machine will start mining again.
Hi, can i found a block with a usb-stick miner with 2,5 Gh/s
You can, but
will you? Probably not, the odds are way against you.