Reinstalling wouldn't solve the problem because uninstalling wouldn't have removed the profile at ~/.mozilla/. While seamonkey comes with a default profile it will write to ~/.mozilla/ when you start it the first time, if a profile is already there it will use that instead of writing a new one.
I'd suggest export your bookmarks, take a snapshot of addons --so you'll know which to reinstall-- then delete the profile. Then restart Seamonkey.
rockedge's advice should also have worked since --in the absence of instructions-- renaming the profile folder would require Seamonkey to create a new one. There seems to be something wrong with your current set-up. You should be able to change your 'Home' page: Menu>Edit>Preferences>Click the Browser Button on the Left. Select your Home page via the bottom panel on the Right, one of whose choices is Use Current Page**.
The default name for mozilla & palemoon's profile folder is 'profile'. But they can be started with a wrapper such as:
#!/bin/sh
#LAUNCHDIR="$(cd "$(dirname "$0")"; pwd)"
LAUNCHDIR="$(dirname "$(readlink -f "$0")")"
mkdir "$LAUNCHDIR/secure" 2> /dev/null
LD_LIBRARY_PATH=$LAUNCHDIR/:$LAUNCHDIR/extralibs${LD_LIBRARY_PATH:+:$LD_LIBRARY_PATH} "$LAUNCHDIR/firefox" "$@" -profile "$LAUNCHDIR/secure"
In the above, a folder named 'secure' is created and the last line (it may have been broken by the display; it begins with LD_LIBRARY_PATH= and ended with '-profile "$LAUNCHDIR/secure") instructs it to use a profile folder named "secure".
Multiple profiles can be created; and the browser can be opened using any by starting it via different scripts rather than via its binary.
I think that there's a way to create have multiple profiles without the use of scripts; but I don't know how. It may require an addon.
Edited after breakfast 
: Booted into Seamonkey 2.53.11.1 which I have as a portable either having updated from MikeWalsh's, viewtopic.php?p=12289#p12289 or by substituting the contents of a tar.gz downloaded from Seamonkey, https://www.seamonkey-project.org/releases/ for the corresponding files and folders in portable 2.53.8.
Multiple profiles can be created by opening Toolbar>Tools>Switch Profiles, Click Manager Profiles, Click Create Profile. The GUI walks you thru the process with explanations. I didn't create one. But from the initial display it appears that once you have more than one you can choose which is the default. And later in the creation process there were instructions about how to switch between profiles.
** Another choice is to select "Use Current Group". Seamonkey has an addon named Speed Start. I think it can be selected. I don't use it. Rather, I installed the Classic Firefox Addon Archive, https://github.com/JustOff/ca-archive without which I don't know if Speed-dial addon would work. During the install it reports it won't work with my version of Seamonkey, but it does. It is selected as the opening page by choosing it from Use Current Group.
