[HELP] RAM Upgrade, OSX Problems!

Just installed some new RAM, upgraded from 2GB to 4GB, system was running slower than usual so thought i'd upgrade and i am seeing a bit of a difference. I installed the RAM and originally could only boot into safe mode, i reset PRAM and it booted up ok. But i noticed when it logged in i had a few question marks on my dock Applications/Documents/Downloads folder and that all the icons on my desktop are not showing, some are but not others. The ones that are showing like images are for some reason default to open using safari.



As well as the dock and desktop problems the icons are also not showing next to the names in the sidebar on my finder, like the Applications folder, my username etc.



One other thing i've noticed is the font when using firefox on certain websites is very small and different to what it usually is, same on the mail app.

I've tried fixing permissions
deleted the plist finder and dock files

Still nothing, i wouldn't really like to re-install because i currently have lion installed 10.7 and the disc i have is 10.6 and i think that if i downgrade i loose all my files? I may be wrong but i can't lose my itunes stuff as it's quite a lot.

Anyway has anyone got ideas for me or ever come across this problem before?

Thanks