70 C for that card's GPU is borderline high.
Did you also clean the card's heatsink with a small brush and a can of compressed air? And if it has internal air passage ways, then use a pipe cleaner to make sure it's thoroughly cleaned.
Also, reseat the card making sure it's firmly seated at both ends with no looseness, the fan is running at its design speed, and the fan & heatsink are securely mounted.
If those do not help, and you did a clean reinstall of XP, then see if the same problem happens with the card installed in another system. If it does, then the card may be bad.