Did that Latitude CP Laptop originally had Windows 2000 on it?
I remember AFAIK a 233MHz processor, <10GB HDD, 96MB/128MB RAM.
If so, Win XP needs at least 256MB to surf the Internet and general usage, otherwise you will have a sluggish machine plus other problems.
Tasks Functionality Amount of RAM
Enough to Boot Absolute Minimum 128 MB
Word Processing Barely Functional 128 MB - 256 MB
General Computing/Web Surfing Functional 256 MB - 384 MB
Gaming/Music Optimal 384 MB - 512 MB
Heavy Graphics/Gaming Smooth Sailing 512 MB and up
IMO, I believe that your Dell CP cannot be upgraded to handle those requirements.
Try reinstalling Win 2000 and you may resolve your screen problem.