My computer is messed up I can't dl anything?

My mom downloaded some type of conferance thing on the pc and soon as i tried to get on yahoo messenger it no longer goes! This sucks! so I tried to delete it and download it again nothing happens then all of a sudden my norton goes off says the system can not scan something and i also had comodo since norton is a 2005 version i know its old but comodo was great untill my i found out it was disabled then i enabled it and it said a cpf-something-.dll can not lad the program. it could not be repaired either! I tried to run spybot it didn't repair so what i did was copy and paste the file from one folder to where it was missing. Found out it worked on comodo then it still showed an error says need attention corrupted program again. Tried to dl online amor and it allowed me to dl but when i tried to open it up in taskbar it had a problem. my system restore for windows xp not working right.