lag problem?

Recently my Western Digital hard drive crashed and I got the same one because of the warrenty. After I finished installing everthing again I get this strange lag. Like i'd open up opera but it wud take 20 seconds to respond. And some other problems that might be related are. Norton system works 2005 doesnt work on startup. I mean it loads but the little "X" pops up and says auto protect disabled. I have to enable it everytime I startup .
Also when I open up My computer it just does that animation for searching for files and does nothing. I exit it and wait a while and I can open it up fine. Also I dont know if this should go here but, When I try to play half life 2 and while it tries to unlock the files for playing it frezzes and my mouse I cant move. I have no idea what I did wrong. Any ideas?

Specs:


Gigabyte k8-ns pro
1028mb pc-2700
Sapphire Radeon 9800 Pro 256mb 256-bit DDR AGP
Amd Athlon 64-bit, Newcastle s754, 3000+, 2.01ghz
1xWesternDigital 160gb 7200rpm, SATA master
1x maxtor 5gb slave
Sound blaster audigy 2
Acer AL1715B 17''
600w demon