Had some spyware that I removed and scanned with avast to check for viruses too, but i keep getting the “no anti virus program detected” pop up thing in the system tray! Not sure how to fix this or if I am still infected!
Sometimes, Windows Security Center stops recognizing your antivirus or firewall… So, check your system time and date and also http://forum.avast.com/index.php?topic=23457.msg193534#msg193534
See also: http://windowsxp.mvps.org/repairwmi.htm
I tried that but it still doesnt recognise it! would it be worth un-installing it and re-installing it?
Welcome to the forums, bonkersdan 
Before trying an uninstall, try doing a repair of avast.
The below is for XP but other Windows OS will be similar.
To do a repair of avast :
Control panel > Add/remove programs > click once on avast to select it > click on Change/Remove > scroll down the left pane and click on repair > click OK> follow directions