Is the Power Adaptor that you have faulty? I have two slingbox solo products and both have failed AC Adaptors. If you have purchased your Solo within 2 years, they should replace free of charge if you call support on UK: (020) 7294 0157.
If not, you can buy one here: http://uk.slingbox.com/go/buy - from what I understand the product is despatched from Europe.
If you are within the 2 year warranty period, but purchased the slingbox over 90 days ago the guys in support will need to take a payment of £19.99 to open the replacement "ticket" but refund the value on the call. I am told this is then authorised by Slingbox Marketing but as this is a known fault it should be a formality.
You can also buy an AC Adaptor from Maplin which does work for me. http://www.maplin.co.uk/Module.aspx?ModuleNo=49063