It would help tremendously if you told us which error exactly...?
and you have how much RAM?
and you your scratch drive is how big?
and you have what Service pack installed? on which version of XP?
You are running PS4 at it's absolute minimum spec...CS4 won't be fun or productive with 512mb ram.
How old is your system and how large are the files ?
When you had it working you might have had more resources available to to you ( less background programs,....etc ).....If you want to use CS4 I would recommend a new system or at the very least a RAM upgrade.
With the specs you wrote of your computer you mean the following?
Dell "Desktop" right?
Your CPU is a Intel Core 2 du0 processor at 2.53 GHZ?
4 gigs of Ram?
your video card is 512 MB of ram?