Prob with my new comp

hello.
i bought this comp. AMD3500+ sucket(939) Gigabite Mobo k8n nforce4 PCI-E 1024mb kingston and ATI X850XT .
the problem is that after i installed windows xp and antivirus updated the windows from the web and all the pc doesnt work like it suld its really slow and some times its shuts down buy its self . i reinstalled the windows 7 times nothing helps .
plz help me !!!

Which version of Windows XP (pro or home) and what Service Pack in on the CD installer?

What kind of Internet access are you on after loading it? Highspeed or dialup?

What Antivirus program?

In what order are you loading drivers and software and updates?
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Besides that. When you load it, make sure you load NTFS and format.
--Do NOT go online yet--
Load chipset drivers first
then video
then other drivers
Then antivirus
turn ON whatever firewall you have whether part of the antivirus or the windows firewall.
Then go online and do the antivirus updates
then do all XP critical updates and patches

If it still wants to behave badly. Check that all your BIOS settings are right. Cache settings, CPU speed and multiplier settings. That your RAM is installed right. Check if your mobo has any BIOS updates that look relevant.