how do i disable the start button on the taskbar using registry?

I advise you not to try. It makes the machine unusable.

To disable the Windows key, follow these steps:-

1)Click Start, click Run, type regedt32, and then click OK.

2)On the Windows menu, click HKEY_LOCAL_ MACHINE on Local Machine.

3)Double-click the System\CurrentControlSet\Control folder, and then click the Keyboard Layout folder.

4)On the Edit menu, click Add Value, type in Scancode Map, click REG_BINARY as the Data Type, and then click OK.

5)Type 00000000000000000300000000005BE000005CE000000000 in the Data field, and then click OK.

6)Close Registry Editor and restart the computer.

To enable the Windows key, follow these steps:-

1)Click Start, click Run, type regedt32, and then click OK.

2)On the Windows menu, click HKEY_LOCAL_ MACHINE on Local Machine.

3)Double-click the System\CurrentControlSet\Control folder, and then click the Keyboard Layout folder.

4)Right-click the Scancode Map registry entry, and then click Delete. Click Yes.

5)Close Registry Editor and restart the computer.