What to try next

Hoping someone can offer a suggestion as to what my next step should be in trying to get my system back to "normal".
Xmas day, system was acting sluggish so I rebooted. The user login screen came up fairly quickly, but after that, loading the rest of the way so slow, slow, slow. Once there (or so I thought), the system was all but non responsive. Clicking on anything didn't do anything. I rebooted in safe mode with networking, things work as they should (of from what I can tell they do).
I have run a chkdsk /r, it stated there were errors, which were corrected, it stated. I have tried booting normally with minimal drivers and that works. I've checked the event log to see if something stands out. There was an error at the same time when this all started, stating following boot-start or system start drivers....with a rather lengthly list of items that couldn't start. I would prefer not to do a reformat if at all possible.
My system is a Dell Dimension 4600 P4, 2.66 GHz, 1.25 RAM. I've run CCleaner and also have Windows Defender and Norton running.
Any suggestions would greatly appreciated. Please let me know if you need more information to make suggestions.
Thanks in advance for any help!
Deanna

 

The first step around here seems to be to check for malware. here is the starting point:
http://forums.majorgeeks.com/showthread.php?t=35407
Hope you get your prob fixed