Very Poorly Server...! Help Needed Desparately

Hi folks. My Sevrer's really struggling. have 2x1G drives in there and 2x2G drives too. Remember doing research at the time when fitting them (working HD models, jumper settings etc) However, seems to be going belly up. Here are some snaps of the errors - it seems to be two drives that are cuasing the problems:

Also attached is logs for these drives from Home Server SMART Add in.

Now - couple of months ago, followed some advice i'd read about running checkdisk on the two drives. I remember this not going so well - with errors etc.

I'm now thinking just replace those two drives with new ones. so:

1) Would anyone offer any advice about the errors indicated above

2) Best way to go about installing two new drives? i.e.:

Which drives to buy (one is the system disk)

Best way to go about installation so don't loose any data.

When I first got my EX495, I was chuffed. But over the years I'm slowly coming to regret it....!

Thanks for any help anyone can offer.