Though they've been offered pots of money for a reunion tour, the chances of ABBA getting back together are probably dead in the water. Enter "Sing-a-Long-a Abba" to end the 25-year drought of super-Swedes in platforms and nylon. After a successful six-year run in London, "Sing-a-Long-a Abba" is making a whirlwind tour of the United States. It's like a giant ABBA karaoke night -- a live band in all its Nordic beauty playing the songs under a big screen for the worshipping audience. And, yes, someone will be crowned Dancing Queen. While not featuring any of the original members, this show promises the most ABBA-infused song and dance this side of "Mamma Mia!" At the Landmark Theater Friday, July 20, at 8 p.m. Tickets are $30. 646-4213.