I have a 1600 non turbo diesel and having real problems with starting

Its had a new starter and dont know if i now need a new battery or alternator. The connections were loose on the live wire connected to the battery but still having problems starting. Charging the battery dosent seem to help much either.
It turns over ok and does eventually start but takes ages.
Also the glow plug light flashes for a very long time before going out.
HELP !!!!!!!!!!!
Thanks
Cherryboo