ArcMap Crashing

Hi is anybody experiencing a strange behaviour from ArcGIS destop - ArcMap. I've been using only postcode sector and joined it with my values - usual stuff - and suddenly when trying to displaye the values through different symbology I get completely strange figures 402589785 (something like this) even though the max I can see in attribute table is 2000 the figures are displayed. There was only 5 of them but I was missing about thrid of my true values. When I was trying to fix it or rather to understand it the GIS crashed on me. This is the second time this afternoon when looking at the same stuff. I even restarted the PC but obviously didnt help! so annoying! and Strange!

thanks,Martina