Why can't I delete all partitions on a flash drive in Windows 7?

There's no need to install any third-party programs, Windows already includes everything you need. Just open up command prompt and enter the following commands in sequence:

DISKPART
LIST DISK

Select the disk that you want to correct. Example: I want to remove all partitions on Disk 1:

SELECT DISK 1
CLEAN

If the CLEAN command doesn't work, try RECOVER.

Disk 1 will be recovered as one complete disk.

FORMAT <option>

Where <options> represent what formatting method you'd prefer. Alternatively, use QUICK.

Try the software MiniTool Partition Wizard.

I've used it before to create and delete partitions on flash media. It may work for you, and it's free.

MiniTool Partition Wizard Home Edition is a free partition manager software designed by MiniTool Solution Ltd. Our partition manager supports 32/64 bit Windows Operating System including Windows XP, Vista and Windows 7. Home users can perform complicated partition operations by using this powerful yet free partition manager to manage their hard disk. MiniTool Partition Wizard Home Edition is designated for home user only.

• Support Windows 2000/XP/Vista/windows 7 (32 bit & 64 bit) operating system.
• Support RAID.
• Extend system partition to maximize computer performance.
• Manage the hard disk for substantial performance increase.
• Create, Delete and Format partitions with simple steps.
• Disk Copy to protect or transfer data.
• Support disk and partition size larger than 2 TB.
• Convert partition format from FAT to NTFS.
• Partition Copy: Copy the entire content of one hard disk to another.
• Copy Disk Wizard: Copy the entire hard disk to another without having to reinstall Windows.
• Disk Map - Visually demonstrate your disk/partition configuration; preview the changes before applying.
• Hide/unhide partition, set active partition, etc. - Change partition properties easily.
• Explore FAT/NTFS partition.
• Set partition as primary.
• Set partition as logical.
• Rebuild MBR.
• Disk Surface Test.
• Partition Surface Test.
• Change Partition Serial Number.
• Change Partition Type ID.
• Hot Extend Partition without reboot. NEW!