New Mobo, Desktop wont load

Hi, today i upgraded my computer's mobo and turned it into an AMD athlon 64 3800+. Dual Core. Everything was fine after i installed the windows, even after all the drivers was installed and my router and internet was hookep up it was fine. The problem happened after i installed avast and told me to restart my computer. First it wouldnt boot and keeps restarting. Then when it finaly stoped restarting (when i pressed Last known good configuration that worked) my desktop would not show. It showed for 2 seconds and the start menu and items would be gone *cries* even the right click wouldnt work. After that i used ctrl alt delete to run programs and uninstalled avast. It still have no use and my desktop just wouldnt come up >_< PLEASE SOMEBODY TELL ME WHATS WRONG. i hope there can be a very logical and simple explanation to this all =[

 

whenever my desktop doesnt show up i pres cntrol alt delete and start a new task labeld "explorer.exe" without quotes

 

thats a very nice suggestion and i dont see that process running. I tried your idea but my desktop wont come up T_T

 

well i guess thats my problem. the process "explorer.exe" wont load. i tried on my other computer and it has that process. =/ im so down now. it cost me 300 dollars to buy this and its causing me grief. can somebody please shed light?

 

im sorry but i must repeat. i cant manualy start up "explorer.exe" and im sure its not a virus because the only website i went to after i reformated my computer was avast.com for the firewall.