Can pull up inbox mail, but can't get into any mail?

no PC strated, no OS stated
no application stated, just the wild and unknown, "compose"
(I use Thunderbird to compose email)

I guess you are using email, (not mail) but email online or using email client. application? outlook or? 100s of others>?
no email service provider stated, is this gmail.com or any of 1000 others?> I can't guess.
if using a browser to see on line email first tell the helper what browsers it is after all IE6, to 10 are now banned on line, and e11 on a few.
sounds to me (wild wild guessing) your PC is infected.
or the browser is all messed up, or banned, as XP is.
try running free CCleaner, with the browsers all closed.
the try again.

Open the Compose page
In the From box, keep the return address automatically filled in by att.net Mail, or select a return address from the pull-down list.
The Contacts tab (to the right of the Mail tab) connects you to your Yahoo! Contacts, where you can select a contact from the list on the left, then click the contact's email address on the right to open the Compose page, with the contact's address automatically displayed in the To box.

Auto-save to Draft Yahoo! Mail Classic now saves the message you're working on (in Drafts) so you don't lose it in the event of a power outage, connection interruption or computer problem. And as always, you can save the most recent version by clicking Save Draft. Once you click Send to send the message, the draft is deleted from Drafts. To review it after that, just look in Sent! Downloading In most cases, downloading now requires only one click-on the attachment name in the message header. Stationery! Now you can choose the perfect background for any message. Click the far-right button on the Rich Text toolbar to view all your colorful stationery options. Message Header We made the From, To and Date information at the top of each email easier to read-and added the option to flag the message in the upper-left corner (click the flag). To view a message's full header, just click Full Header in the lower-right corner. One-click "Flag this message" Organize your most important messages! Just click the dot in the new Flag column-it's one over from the check-box column. If you're in the middle of reading a message you'd like to flag, click the gray flag in the upper-left corner of the window. Finally, if you want to see all your flagged messages grouped at the top of your Inbox (or any other folder), just click the flag at the top of the column. Bingo! Inline Signature If you've created a signature in More Options, you will now see it each time you open the Compose window to write a message. If you don't want to include it, just delete the signature text as you would any other text in your email. Or, if you'd rather not include a signature in any of your emails, click Options, select More Options, and under "Management", click Signature. Delete the text in the window to delete your signature, then click Save. Forward as Attachment You can still forward a message as an attachment by holding down the Ctrl button on the keyboard and clicking Forward. Mark as Unread When you're viewing a message, you'll now find Mark as Unread in the upper-right corner of the window. We did this to reduce clutter in the top middle area. Bulk Folder = Spam Folder We updated Bulk to Spam. Because, well, that's what it is! It functions just the same as before. Address Book = Contacts "Address Book" is "Contacts" in the new Yahoo! Mail Classic. Message Encoding You don't need to change message encoding through your browser anymore. Instead, just use the encoding pull-down menu in the lower-right corner of the page while you're viewing the message. In addition, you don't need to change the browser's encoding when you compose emails. Just type away! Rich-text/Plain-text link On the Compose page above the message window, you can click either Rich Text or Plain Text to select the format you prefer. Cc: on the Compose Page You don't have to click a link to open the Cc: line anymore. Now, it's always there--just waiting for whoever else you want to send your message to. :o) Folder Renaming and Deleting Rename and delete your personal folders more easily by clicking the folder on the left, then clicking either Rename or Delete next to the folder name at the top of the page. Flagged message and Attachment sorting Just click the column headings to group messages by what's flagged or has attachments. News Module Now you'll see the same News Module that currently appears in the all-new Yahoo! Mail. Mark as Spam Marking a message as Spam now moves messages to the Spam folder instead of Trash. Screen Reader Accessibility Yahoo! Mail Classic offers enhanced accessibility to screen readers.
And...

Features We Removed Details Today's tip Today's tip was on the Welcome page. Send an e-card The link on the Compose page is gone, but you can still send e-cards by visiting http://www.yahoo.americangreetings.com/ Avatar display You won't see your Avatar on the welcome page anymore when you log in. Instalist We've taken out the option to create a mailing list for recipients, which was on the "Message Sent" page. Here's how to create a category if you want to send to a group. Online Presence Indicator We removed the icon showing whether your contacts are online or offline with Yahoo! Messenger. Quickbuilder Was a way to scan your mailbox for people you hadn't added to your Contacts yet. It's gone, but anytime you send email to a new contact, you have the option to Add to Contacts on the "Message Sent" page. Add Mobile Alert If you want to get an alert on your Mobile Device when mail from a specific sender arrives, make sure your device is registered. And now, instead of clicking Add Mobile Alert (which used to appear in the From/To info area above an email), go to the Filters section of More Options to set this up. "Add to My" button We removed the icon at the bottom of the Inbox that enabled you to add an Inbox preview to your My Yahoo! page. Keyboard Shortcuts We removed Check Mail, Compose, and other keyboard shortcuts. (e.g. Control + Shift + P for Compose.) Save Message Text Gone: the link in message view that saves the text of an email. Attachment Preview This feature gave you the chance to view both Microsoft Word and Excel files as HTML pages. Now, it's gone-but many browsers give you the option to view (Open) an attachment without downloading it. To start, just click the attachment's name in the message header. Messenger-with-Voice Integration

Hi,

A Solution exists on yahoo help page, please visit this page 

http://help.yahoo.com/l/us/yahoo/mail/classic/technical/technical-10.html

Thanks,

Try optimizing your Internet browser. Here's how:

* For Internet Explorer:
1. Run Internet Explorer and click on 'Tools' menu.
2. Go to Internet Options and locate the Browsing History section.
3. Click the 'Delete' button and delete the Temporary Internet Files, Cookies and History.
4. Close the Internet Explorer and re-open it.
5. Access your e-mail.

* For Mozilla Firefox:
1. Run Firefox and hit 'Tools' menu.
2. Go to 'Clear Recent History' and click the drop-down arrow for 'Time range to clear'.
3. Select 'Everything' and then hit the 'Clear Now' button.
4. Close and re-open Firefox
5. Access your e-mail.

At the top left there's a yellow button that says New. Click on it and you can compose an email to someone.

you can ask yahoo to block that a/c

The word search the web is covering my compose box

just reset ur internet explre webv setting clar cookis and delete temp file

AOL Inbox Mail I need to Delete...Have over 25,000 Without Deleting 1 at a Time...HELP!