I have a external HD (500 gb) it has a lot of my data.Some virus/error might have creeped in it as now when I plug in the port it asks to format the drive that will make me lose all the data.Is there an alternative to format or a solution to this problem?

Your problem can be a virus or your hard disk is going to crash. Some corrupted files may have caused this or you could have accidentally drop your hard disk. Try plugging the hard disk to various computers or laptops and see whether they can read your hard disk. If they can read your hard disk make sure they do not prompt you to reformat. If they never ask you to do so, you can retrieve the data first before reformat. Or you can reformat lightly meaning reformat your disk less than 2 times. This make it having a higher chance to recover your data.

Did not really help.I get this error "Data error: cyclic redundancy check".Please help.

I scanned using it, but it found no infected file.please help

Now its giving me error message "drive inaccessible due to i/o device error".Please help.

I don't think you have much choice left but to reformat it and later use a software to try and recover most of your data. i will ask some senior and expert daniweb posters better than me to try to help you first, reformat the hard disk is the last option so you wait for a few more days first

You don't have to format the disk before recovering your data.

try this recovery software: http://www.piriform.com/recuva/download

or this: http://www.powerdatarecovery.com/

You will need some temporary room for all the files that you need to save, so you might have to borrow or buy another usb-disk for that purpose.

Later, when you have copied all your files, you should run a full format on the bad disk, to map out all the possibly bad sectors, before copying data back to it.

Hdd regenerator free version might be able to tell you what the cause of the problems is. Unfortunately it will only repair 1 error unless you buy it. http://hddregenerator.net/

Another idea. Format the drive but don't put any data on it. Then use recuva to get your data back. Recova is free but is not as capable as hdd regenerator. http://www.piriform.com/recuva/download (scroll it down a bit and click on the green link that says "Download from Piriform.com)

Damn, didn't get back soon enough to edit my last post.

I have experimented with Recuva.

If the MBR (Master Boot Record) of the partition is readable then Recuva can get the data back without a format.

If the MBR is unreadable then Recuva can't access the partition, but, if you do a quick format on said partition, and even after windows has said it will erase all data, Recuva can STILL get your files back.

I have a hard drive belonging to a customer that I am experimenting on. It has 3 partitions on it.

Partition 1 is readable by windows but there are no files on it that he wants.

Partition 2 is unreadable by windows but Recuva can read it as the MBR is in tact. There are no files in it that he wants.

Partition 3 is unreadable by windows and the MBR is corrupt so Recuva cannot read it. I have just done a quick format on it and Recuva is now recovering the files he wants from it (although it's gonna take a good few hours to complete).

The original poster now wants a software to detect his hard drive. His external hard disk is now not reformatted, but when the hard disk is plug into a laptop, it cannot be detected. The laptop keep on asking him to reformat the disk because the disk is having problems. Maybe due to hard disk crash or corrupted files, any softwares to recommend to solve this. Like making it detectable by the computer.

I am not sure about recuva, but the second link I posted (powerdatarecovery), is able to detect the harddrive even if it isn't formatted, and even if it have defective sectors in the partition table.

I suggest you try it. (it is free for private use) :)

I have found that this problem was not answers perfectly, so I decide to tell the data recovery solutions, about the usb recovery, this article contains all the data loss situation, I hope it can help anyone who comes across the same problem. Please refer: USB data recovery

commented: your answer does nothing to help the OP, it's just an advert and nothing more -2