Unknown information:
MacOS X version
iBook model
In addition to ElDiabloConCaca's request ...
... boot from the installation CD / DVD, run its copy of 'Disk Utility' - performing a 'Repair Disk' (at least twice), and then 'Repair Disk Permissions' (at least twice) on the iBook's internal hard disk drive, hdd. Next, reboot the iBook from its internal hdd. Please post your results.
Note: The installation CD / DVD should be the same MacOS X version: Jaguar (10.2), Panther (10.3), or Tiger (10.4), as is on the iBook.
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'... the white bar', is the 'menu bar'.
If you have access to another MacOS X based Mac, consider backing up the iBook's contents. One way is described here:
01. Turn OFF the iBook, and connect it to another Mac via a Firewire cable.
02. Turn ON the iBook with the 'T' key pressed, and kept pressed, until the Firewire symbol appears. On the other Mac's 'Desktop' an icon of your iBook's hdd should appear.
03. Copy the contents of the iBook to the other Mac. Specifically, the iBook's Home folder(s) and at a minimum - select (1) '/Library/' folder's.
04. Drag the iBook's icon to the other Mac's Trash can (now 'Eject') symbol.
05. Disconnect the Firewire cable from both Macs.
(1) - Address Book Plug-Ins', 'Application Support', 'Contextual Menu Items', 'Image Capture', 'Internet Plug-Ins', 'PreferencePanes', 'QuickTime', 'Screen Savers', 'StartupItems', 'Workflows'. Why?, because some applications add files and / or folders (of items) to some of these folders. Without these items installed, some applications may not launch, and / or operate correctly.