Avast Internet Security...won't open

[vix]

Today I realised that my avast internet security program will not open. It's ages since I opened it to scan, I just have it on automatic and have had it for 18 mths.  It's got me a little worried.   What can I do to make sure it's okay?  It won't open in sandbox either. 
thank you.

[vix]

hello there I am still having problems and canot open Avast. 

it gives me an error report which says
AppName: avastui.exe    AppVer: 8.0.1489.300    ModName: kernel32.dll
ModVer: 5.1.2600.6293    Offset: 00012fd3

and then produces an extensive error report. 

any ideas what is preventing me opening up my avast software?
random other things are now happening too, such as being unable to download updated drivers for my printer.

many thanks

[CraigB]

You could try a repair of avast via uninstall programs follow by a reboot but if that doesn't work I suggest you download the avast clear tool and a new copy of avast http://forum.avast.com/index.php?topic=142936.0 and perform a clean install.