DISKPART> list disk
This will list all your drives, including the SD card; you need to be very careful to select the SD card and not your hard-drive, usually it is easy to recognize the SD card because its size is only a few GB (depending on the card you use) as compared to the HDD which is usually much larger.
DISKPART> select disk 1
Disk 1 is now the selected disk.
DISKPART> list part
......... list of partitions .........
DISKPART> select part 1
Partition 1 is now the selected partition.
DISKPART> delete part
DiskPart successfully deleted the selected partition.
Now you have to repeat the last 2 steps (select/delete) for as many partitions as you have, the default is 2 partitions so normally you have to do this only once more. After the last partition is deleted, you create a primary one and exit:
DISKPART> create part pri
DiskPart succeeded in creating the specified partition.
At last, you remove the card and re-insert it and windows will prompt you to format it; no need to do a full format, quick format works great. This process works very well for me, I've done it a lot of times but it is quite involved.
Last night I ran into another great post on the excellent Raspberry Pi Spy website about how to format Raspberry Pi SD cards using SD Formatter. I won't detail the steps here, the article I mentioned is really good and I do want to thank Matt for such a great post!