Why is my start menu at the top

You can move the taskbar back to the bottom by clicking on it, and dragging it down.

The cause for all your symptoms may be malware. You should boot into safe mode with networking. Download, install, and update malwarebytes. Then do a full system scan.
www.malwarebytes.org/

There are two problems here, why is the start button white? AND why is the start menu at the top? I can gather that an automatic update has changed the settings of the computer. To reverse this automatic update and the changes it has made, the easy way is to try a system restore. This turns back the clock on the computer to the time before the problem started.

Restore does not erase your personal files and is reversible.
click start
click all programs
click accessories
click system tools
click system restore
check the box that says restore my computer to an earlier time, click next
select a bold date on the calender, a date before the problem started, click next
follow through with the restore directions
restart the computer after it finishes
if the system restore does not work, select an even earlier bold date on the calender and repeat the procedure
try this with at least four earlier dates before giving up and trying something else

Once a system restore has finished, the settings of the computer should be back to normal, the start button should be green again.

Now to move the start button back to the bottom of the screen. It's actually the whole task bar that has moved. To move it back, you first need to unlock the task bar:
point at the taskbar
right click on the bar
left click properties
un-check the box that says: lock the taskbar
click apply, click OK
The taskbar is now unlocked

close all programs running on the desktop
point at the middle of the taskbar, or just to the right of the middle
hold down the left mouse button, drag the taskbar to the far left of the screen, then down to the bottom of the screen
release the left mouse button
you might need to try this a few times before you get the taskbar to move, but it will move with some practice.
now point at the taskbar
right click on the bar
left click properties
check the box that says: lock the taskbar
click apply, click OK
now the taskbar is locked to the bottom of the screen, the start button is back on the bottom

No valid windows update would alter the settings like that.

^+1 The XP forum is experiencing an acute state of a FUD outbreak in recent days.

There have been a rash of several problems springing up since MS recently changed the automatic updates and AU website:
a. The computer loses the audio drivers, the drivers need to be reinstalled.
b. The computer loses themes settings, the task bar changes to white or gray
c. The computer desktop icons disappear
d. The computer no longer recognizes a disk in the CD or DVD drive
e. printer drivers lost or corrupt
f. after update, boots to a blue screen, after installing SP3 from update website

We could attribute this to malware, which it very well could be, but computers with the automatic updates shut off permanently are experiencing none of these assorted problems. Also, scans of computers with these problems are turning up negative for malware. Also, using system restore is correcting the changes that have occurred, and is a good solution, it does not work every time, but most of the time it does.
Not that I doubt malware is going on everywhere, and that installing good security is a necessity. Nobody would question that.
Tens of thousands have turned off automatic updates, because they are weary of the surprise changes to the operating systems. This includes the IT professionals at Cuesta Collage and many other professionals across the globe. I too, have turned mine off, and no more surprises.
While it used to be AU would make the system more stable, indications are for XP that the opposite has become true.

The fact the Mr. Badge lashes out at other members of the forum with insults and obscenities is a mark of highly unprofessional character. He, like everyone else, is welcome to disagree or to offer his / her own solutions. This freedom it appears is not enough for him.
I have replied to many posts after other members did not reply, including Mr. Badge. I offered insight and solutions to posts that would have otherwise gone unanswered or unsolved. In many cases the problems were solved, and selected as a best answer. But he would prefer to allow others to post a solution before attacking.
The solutions I have posted are valid, and tested, there is more than one method or solution for each problem posted here. Some do not recognize that fact; they would rather kill the messenger rather than the message be heard. Others, open minded, will be willing to consider another perspective.

None of us are right all the time. In the spirit of curbing misinformation, it needed to be pointed out.