Canon camera won't accept SD memory card

Question edited for clarity.

Your memory card is too big and beyond the capabilities of the camera. 512Mb is recommended. Page 34 of the manual

http://gdlp01.c-wss.com/gds/8/0900001188/01/PSA540_530CUGad-EN.pdf

..

The A410 works with SD cards. Your 8GB card is an SDHC card and won't work in devices not designed to use them. You need to use SD cards, 2GB and smaller.

Hi,

Please try to copy all the contents of your SD card to your computer. Then format the SD card and try it again on your camera.

If it still can't be detected, try another SD card.

The following link describes the maximum SD card size for your camera.
http://www.mymemory.co.uk/compatible-memory/Digital_Cameras/BenQ/BenQ+DC+E53_Memory_Cards


The following is from their site:
BenQ DC E53 BenQ DC E53 Memory Cards (SD Card) & Accessories

The following digital camera memory cards are compatible with your BenQ DC E53. Every digital camera memory card we offer is manufactured to the highest standard and carries a 2 year minimum warranty.Your BenQ DC E53 accepts SD Card cards.The largest SD Card card you can use in your BenQ DC E53 is 2GB

So you can buy up to 2GB SD cards.

From page 145 of the A520 user manual, it appears that the largest SD memory card that this camera is able to use is a 512MB SD memory card. The manual is dated "2004", so this size limitation is not unusual for a camera of this era.
If you've purchased anything larger, there is a good chance that it won't work with this model camera.

The Canon A430 uses MMC and SD cards. While SDHC cards will fit into the slot they are electronically incompatible and will not work. You need to use SD cards, 2GB and smaller.

The A430 works with MMC and SD cards. It will not work with SDHC cards. You need to use SD or MMC cards, 2GB and smaller.

Most new 4GB and larger cards are SDHC cards (look on the card). Although they look exactly the same as a standard SD card, they are not. Unfortunately, there is no way that these cards will work with your camera, as it was designed before the SDHC format came out. As you've dsicovered, 2GB and less are standard SD cards, and will work with your camera.

There were a few standard 4GB cards produced a few years ago, most notably by ADATA (I have one that I use in my A620). Unfortunately, these are rare now, and are somewhat expensive if found on eBay.

More likely one of the spring contacts in the camera that connect to the SD card has become weak causing the problem.

Try reformating one of the cards