A repair install may do the trick, but it does have some risks although it is likely things will go just fine. But I would rule out other things before going that route.
What model Celeron do you have? If you are running an old s478 Celery that may simply be your problem, pending an all clear of your HJT log by the security experts. An old Celery like that probably can't keep up with all the programs you are loading. You have a lot of programs loading at startup.
How does CPU usage look in your task manager? Is it at 50%, or even near 100% all the time?
Also if you're using Adobe reader 8 there has been a very bad bug in the updater for a long time causing the CPU to stay around 50% usage and slowing the whole system down. Look in task manager to see if adobe updater is using around 50% CPU time.
8.1 Pro 64bit
AMD FX 8350
Asus Sabertooth 990FX R2.0
24GB GSkill/Corsair 1866MHz
2x XFX 6870 1GB
SSD - OCZ V4 128GB/Kingston 120GB
HDD - 3TB/2x 750GB/500GB/250GB
Cooler Master HAF 932 Red
CM Hyper 212 EVO w/2x SickleFlow 120mm Red
Logitech X540 5.1 Surround
2X Acer 23" LED - Eyefinity: 3840x1080
Microsoft Sidewinder x4 KB
"The significant problems we face cannot be solved at the same level of thinking we were at when we created them."
- Albert Einstein