I need to reconfigure my netgear adsl2+modem dm111p v2

Just pull the leads out, including the power adaptor and put it in the cupboard.

This is a modem, not a router, so Port forwarding is not possible.

See Manual http://www.downloads.netgear.com/files/GDC/DM111Pv1/DM111_RM_23Aug06.pdf

POWER ADAPTER ISSUE

as your provider to send a technician as the powerlevels on the modem are not right

GO TO NETGEAR Router AND START A NEW CONFIGURATION.

i suppose you have to connect modem to router's "source" socket and modem to socket "in wall" then reset and reconfig router and you should be ok

There isn't really much to configure on a cable modem. If the modem is fully recognized by the cable provider (all lights are lit on the modem once connected to the cable (coax) side), then just plugging in the Netgear router's INTERNET connection directly into the cable modem will work fine. If the modem isn't properly recognized, you'll have to call your cable company and provide them the MAC address of the cable modem. The MAC is a 12 digit hexadecimal (0-9,A-F) number that should be on a sticker on the modem itself - it will be listed as six pairs of hex digits. If the cable company doesn't have that particular MAC address attached to your cable account, then it won't work.

check out with your ISP provider ask them to run a line test on your line.
sometime it happen that your line gets a fault.

Hope this will resolve your issue.

Sounds like you need to port forward your router. Go to port forward .com. find your router and follow the instructions. Hope this does the trick for you.

Look for a factory reset button (pinhole) near the power port. Use a paper clip or something to hold it in for about 10 seconds. That might recover it.