If most of the channels are still there it's an aerial problem. (A dud box would simply stop receiving any channels). Signal strengths at your aerial don't remain constant so, if your aerial isn't up to the job, some stations will be there one day but not on others. For a more detailed explanation, please see my posts here:
http://www.theanswerb...y/Question858245.html
It's quite likely that your reception problems are related to the recent violent activity on the Sun's surface. However the root cause is still a poor aerial system. It might be worth trying a signal amplifier (= 'booster') but a decent aerial, such as this one
http://www.maplin.co....e.aspx?moduleno=22523
(which is highly recommended by many people), together with new cabling, might be the only sure way to get decent Freeview reception.
Chris:
PS: If you're in a very poor reception area, you might need this type of aerial:
http://www.maplin.co.....aspx?ModuleNo=221124
PPS: Remember that, unless you live in an area which is now totally digital, your Freeview transmitter is currently operating on reduced power (to avoid interference to analogue transmissions). Things should get better when the digital changeover has been completed.