Please Help with the many problem with my windows xp sp2???

well my computer had several viruses and i worked around all the problems 4 a while, then i got my windows xp sp2 cd and i completly reformatted the hardrive, and reinstalled a clean xp, well i thought it would all be good, but i still have many of the same problems....

1) I have problems downloading some files, like palm desktop, i download it and at the end it always says somthing is wrong. i forget exactly

2) Sometimes the top of my internet explorer screen will turn from blue to black, also my antivirus (trendmicro pccillin alert will come up and i cant read the alert because the majority of it is also black.

3) Sometimes when i click my start menu the programs will be invisible. and sometimes i get the error.. NOT ENOUGH quota to process this command,, and my Cdrive is set to no limit.

I only have an 18GB harddrive but i have 16GB free memory. so im only using like 2 gb of memory.

I haved tried so many things to fix my problems, and ineed some adivce, before i buy a new pc

Please Help with the many problem with my windows xp sp2???norton internet security

You are getting mudlled up with memory and disk space, On your Desktop right click on my computer and then goto properties this will give you box with opertating system and memory, the minimin with Xp is 64MB if it is less than this you need to upgrade it else your graphics card or computer is done

Please Help with the many problem with my windows xp sp2???spyware remove

I hate to tell you this, but your system is way under powered for XP

You need a bigger hard drive, and more RAM.

Win XP uses up 100+ mb of ram plus asks for a page file. your system is just not good enough for it.
did you buy this computer from a major retail? for example DELL?