Hi Hanhan27.
One more thing to check unless you have already factory reset.
Go into settings and applications, then manage applications (or similar depending on your device).
Show all applications and go right to the bottom, you may have an item called "Download Manager", if it is there it is likely that it is disabled, just tap the item and enable it, reboot your device and all will be right in the world.
If it is not at the bottom of the list, and enabled, clear its data and cache, check then just continue with the factory reset if it is still an isue.
Hope you get it sorted.
