I prefer to use a full REPAIR rather than a simple VALIDATE. When you REPAIR in DiskSalv it goes 'the whole hog' and you still get a validation at the end. Maybe it thinks you need a full repair since you have ghosted buttons.
Are you using a disk below 4.2GB? Unusual for an IDE disk to suddenly get Checksum errors, I get them a lot on SCSI but that's because I have cable/connection trouble. IDE is fairly straightforward with a small ribbon and no connectors inbetween.
It might be worth pulling off the IDE connector and putting it back on again though, it can't do any harm and may well make a better contact if the summer heat has tarnished contacts. This was a big problem with the Dreamcast (it could be fixed by using WD40 spray on the PSU connector).
Also download Virus Executor v2.34 to make sure you are virus free (viruses can cause random errors) and maybe check Max Transfer/Mask values.
:-)