Multiple Win-XP problems.

I have been having problems for a few months with my computer. A Dell Dimension E310 running Win XP service pack 3. I seem to be running in circles trying to get it back into a normal working condition. I keep having a pop up ( "svchost.exe - Application error : The instruction at "0x00000000" referenced memory at "0x00000000" could not be written") Or a pop up concerning a script error. Also when I hit F8 to log on in safe mode the screen is split in half so that the info starts at the bottom section of the screen and finishes at the top with part of it missing. The computer seems to freeze up and will not shut down normally. Programs like itunes do not run like they use to. I just don't know whats going on with this thing anymore. I tried to restore back to a previous day and it would not do it. Would it be easier to just use the restore function and restore the thing back to the day I got it? Any help would be much appreciated!!!

My computer did not come with a windows CD. Do I need to make one?