Why Tablet Why?!?!

After trying all day.
Downloading, Deleting, Un-downloading, Re-downloading... why.. ...

If anyone can help me with this that'd be fantastic...
Whenever I use SAI to draw at all it lags!
Like severely lags.

It took me maybe 20 minutes to draw this thing here because of it and before then I have already drew the angel thing... so the dog and the writing took me 20 minutes to do...
Gahhh!
I just wanna throw something!

I can't draw or do anything!
I deleted all of my art files and saved certain ones, like YCH's on my dA sta.sh though.

I really, really need help please.
I feel like I wanna cry right now i'm so frustrated!

I may be the computer i'm using as well... it a 2009 Windows Vista... so maybe? If it was though.. why hasn't it done this before???
Ugghhh... just someone... help..