Massive decrease in speed/increase in Attenuation

I was up at the Admin ofiice for a Society of which i am a member on Tuesday to add machines to the Network and improve Security, and whilst there took a look at the Broadband Stats, just to check that all was fine. Noticed that the connection rate had dropped from 17677 to 5791, but there had been a jump in line attenuation, especially on upstream.
I am presuming this jump is reason for drop in line speed, but was wondering what would cause such a jump in Line attenuation and the best way to get the line performing correctly again.

Original Stats
Down Up
Line Speed 17677 979
Attenuation 16.5 7.2
SNR Margin 9.1 7.5

Stats now (as best i can remember, forgot to write them down)
Down Up
Line Speed 5791 808
Attenuation 20 18
SNR Margin ? ?

They are not too worried about it being fixed right away as only mainly used for e-mailing, but obviously would prefer speeds, back to what they should be.

Is that with same router?

Cuz 2nd set are suspect. Down attn. usually approx. 2 x Up.

Yes is with same router (A Belkin but not sure of exact model) probably 4/5 years old at least.
I know the 2nd set are suspect, which is why i'm querying what may cause the problem.
Would just switching the router of and back on solve the problem?

It might help. I presume telephones still work ok on the line?

Not sure if phones still work, as they don't use the phone that much.
So if they have or had a problem with the lines then could this explain the problem and therfore a restart on the router could sort it out.

If the phone is not working than restarting router wont help but reporting a voice fault should get it fixed